I posted this in r/tennis and several people urged me to post it here.

Addition to the OG post:

a. Playing as many matches as possible will help you a lot.

b. You can DOMINATE doubles matches against beginners and intermediates if you learn proper high school and college-level positioning and movement. Examples: Proper signaling. Australian setup. Net player constantly shifting with the ball. One of my hs coaches was a master at doubles and taught me proper strategy and positioning, which let me easily beat other players that were way better than me at singles.

1. If you're a TOTAL beginner, your racquet does not matter as long as it works. Just get an adult-size racquet and start playing.
2. Practice your form and swings on an off the court as much as possible. You can make serious progress by just looking at a mirror while swinging and comparing it to good players to whom you want to match their form. You want to get to the point where you will instinctively get into your form/swing when you see the ball coming towards you.
3. If you can, get a coach for private lessons where you will learn form, shot selection ... etc for a few months. Practice what you've learned at each lesson as much as you can on the days in between lessons at a court with friends and family. After about several months to a year (depending on how good you are), join a clinic for exposure to as many other players as possible. Do the clinic at least once a week. Since you are not taking private lessons anymore, go to your local court with a friend or family member, a basket of new balls that you got for cheap, and relentlessly do drills that you can remember from your lessons or other drills that will help. Consult YouTube and your clinic coach(es) for drills. A good coach will want you to practice outside of the clinic. Your drilling and point play by yourself and with friends/family is extremely valuable and basically serves as the replacement for the private lesson drills. Hit thousands of high quality balls a day if you are serious.
4. Get very good at quickness, form, and footwork. You want the tennis footwork to be instinctual. The split step and ready-position are your best friends. Mastering the split step will make it hard for people to hit shots past you since you will be ready to move to any direction. Me tennis split-step made me a good basketball player since could never get crossed-up because of my split-step and good base. Good footwork leads to a good body turn, good form, and good shots. Footwork is king. Practice getting fast and accurate feet on a ladder drawn out in chalk or something like that. Do the same type of off-court drill for footwork as you would hitting shots. Train your footwork by asking coaches for specific methods as well as watching YouTube videos and copying good players.
5. Get fit. You can beat a ton of beginners just by being faster. Also by being fit, you are less likely to get tired and start doing lazy footwork and swings, which leads you to losing points. Work out with your soccer and basketball friends since soccer and basketball training are safe bets for tennis players' purposes: running, sprinting, leg workouts, fast footwork, endurance...etc. In addition, work out your shoulders, chest, back and biceps. You don't need to go crazy since most of your power will be generated by your form and not just brute strength. Contrary to popular belief, if you try to play matches out of shape, you will fail unless your technique, shot selection, and strategy is insane. You don't see any fat players on tour, do you? You can still be out of shape as long as you are working to get fit. Don't strain yourself since you making progress will be a gradual thing.
6. Focus on fundamentals, form, footwork ...etc until you are ready to play points. Many players start point play on day 1 and have no idea what they are doing. They end up trying to keep playing points, which is a waste of time if you cannot control your shots properly. Once you are ready to play points, live drills and matches are your best friend. Get comfortable with the entire flow of playing points, games, and matches so that you feel totally calm and comfortable during the ones that really count.
7. Serve progression. (This is just mine. Everyone's will be different.) First, focus on getting your serves in with high consistency while adhering to the proper form as prescribed by your coach or another credible source. Then, focus on adding a small amount of spin to your serves. This spin should be a combo of mostly topspin with sidespin. You want this to be your default serve (for both serves) as a beginner. Your flat serves should never be 100% flat. Most beginners see good players have a giant flat first serve and then a heavy topspin second serve, try to copy it, and end up with a massive first serve with a 5% chance that it goes in and then a neglected second serve that becomes a free set up for your opponent. Focus on making BOTH of your serves the top-side spin combo. This will help the ball get in and add a little spice for your opponent to deal with. If the beginner false flat serve is 100% power and the neglected second serve is 20% power, you want BOTH of your top-side spin serves to be around 60%. This will ensure consistency and mild speed. You may be thinking, "Why only 60%?" Let's face it, even if you could get your 100% speed beginner serve in, that speed isn't really doing anything against someone who knows how to return well. It is a waste of energy for beginners for a stroke that demands consistency. Consistency is king on every shot. A decent serve with decent spin that you can count on to go in most of the time will be your best friend. Double faults are free points for your opponent and your coach isn't doing his job if he doesn't bust your butt for double faulting too much. Once you get good at serving, add power to your first serve for an 80% first serve and 60% second serve.
8. Get good at playing against big hitters by predicting shots. Many players who have little experience against powerful shots, end up doing terribly against powerful players because they get caught up in poorly-timed footwork, a lack of confidence on strokes, and a lack of skill on where to predict the ball will go. Practice the true/mid-way recovery position on your groundstrokes and get good at recovering to hit the next shot in a split second. Get good at reading strokes of your opponents so you can have a general idea of where the ball will go and get set up to hit a confident shot off of their bomb forehands. Just because a player hits hard at you, that doesn't mean you should not finish your stroke. You may want to cut down on your backswing to save time, but everything else should be the same, especially the follow-through. You will do well against big hitters if you learn to maintain SUPREME CONFIDENCE in your shots when hitting back fast balls. Big hitters are usually used to hitting winners and not moving much so they will be caught off guard if you use their speed against them and hit confident shots off of their shots that they expect to end the point. Everything in this point (#8) is VERY HARD to explicitly learn. These skills will come from years of practice if you dedicate attention and time to them.
9. Scare the heck out of pushers. For those that don't know, pushers are usually fast players with bad, but VERY CONSISTENT shots. Their whole strategy is usually to just hit high percentage shots (usually slow with no spin) and wait for their opponent to mess up because most beginners and intermediates are not used to capitalizing on floaters. How NOT to win against pushers: Trying to hit hard and hit winners. Pushers will not miss and they are fast. They will easily get to groundstrokes and be ready for you to mess up. They will also happily just redirect your ball speed right back to you with a low shot with no spin that doesn't bounce higher than your waist. As frustrating as this is, it is THE ULTIMATE tennis strategy (except the bad shot quality). Just ask Andy Murray, who successfully used it on a professional level. There is also a quote from another coach whom I cannot remember his name but he said, "If you can hit 19 balls in during a point and your opponent can hit 20, your opponent will always win" or something like that (I don't remember the exact quote). If you ever find yourself in a pickle, high confidence and consistent shots are your friend and the best way to win matches. How to WIN against pushers: Do not give him any predictable shots. Assume that he will get to any ball that you hit from the baseline because he will. If you can, hit normal groundstrokes or slices with unpredictable spin until you get your chance to rush the net. When I say "rush the net," I mean "RUSH THAT MF NET" off of a good approach shot. You will often get free approach shots from pushers. If you hit your very high consistency approach shot and rush the net, the pusher might panic and give you free volleys that you can put away and win the point. Pushers also usually have no plan when their opponent comes to the net. They don't hit very hard at all so if your approach is good, he will give you easy net set ups. I once had a tournament match where I lost the first set 4-6 and was down 1-4 in the second against a very athletic player with weak and consistent shots, to whom I gave many free points by missing groundstrokes. In the next game, I started trying things because I really had nothing to lose so I mindlessly bum-rushed the net for fun on every point and he had NO CLUE what to do. After that, I rushed the net on every point with good form and good purpose and hit overhead and volley winners on every point. He won maybe 5 points total after I did that strategy and I won the match 4-6, 6-4, 6-0.
10. Racquet choice. For beginners, as I said already, pick up a cheap adult size racquet because the strings and racquet specs don't matter for you as long as it isn't broken since you are learning form and footwork. For intermediates, get 2 good and reliable racquets that you string to your specification. You want to find your favorite string and tension combo because strings make a huge difference. I won't get into that since the whole string type, tension, other specs etc are an entire mathematical research topic that would take way too long to explain. I'd just advise to play around with different types of strings and tensions. For advanced players, you can probably make-do with 2 racquets but 4 is ideal since you will wear the strings down much faster. As long as you don't catch yourself with no racquet, you're probably fine. For intermediates and advanced: pick a racquet that you have demoed and has a good reputation. Look at the big names like the Wilson Blade, Pro Staff, and Burn, Head Speed series, Radical series ... etc. Find one that you like.
11. Take care of your equipment. Military people often say, "Take care of your equipment and your equipment will take care of you" and they are darn right. Do not take your strings into different temperature environments as they will warp and break. Do not slam your racquet ever. You will just look bad and you will possibly break an expensive piece of equipment. Buy shoes with the 6-month sole warranty so you can get two pairs at the price of one if you go through them. Don't mindlessly move your feet to the point where you are wearing down your shoes and wasting money for no reason.
12. Keep calm and have fun. If you get mad you will play bad and if this escalates, you will look like a jerk on the court and everyone will dislike you. It's a game. Have fun. When you are having fun responsibly, you are more likely to do a good job at whatever you are doing. If you are angry and throw a fit after losing a tournament that you paid to enter, take that as a lesson to get better before the next one so you can guarantee that your money will go a long way.
13. Make your opponent suffer. This is the opposite of point #12. You want your opponent to hate playing you so that they will mentally crack and start making a bad strategy or talking down to themselves and losing easy points. If your opponent is a chubbster, you may want to make them sprint back and forth across the court to make them run out of energy during the first 15 minutes of the match. Craft your shots, shot selection, and spin in a way that makes your opponent unable to hit their confident normal groundstrokes (kind of like pushers slicing the whole time and not giving their opponents much speed to feed off of). But you don't want your shots to suck and be all slices and floaters.
14. Tennis is expensive. Take price shortcuts as much as possible. I mentioned a few already like doing high volumes of practice on your own after lessons with your friends and specifically looking for the 2-for-1 6 month outer sole replacement deals on shoes. More include not entering paid tournaments until you are confident and ready, taking care of your equipment, practicing with whatever resources you have, taking care of your body, and paying the HIGHEST level of attention to your coaches at paid (or unpaid) lessons. You should always be doing that last one anyway. I used to do a clinic at a local tennis club for a few years and I eventually left to go to a much better club. However, I still kept showing up to the first club's free walk-on court times for students since I was good friends with the staff and they all just assumed that I was still taking lessons to qualify me for the court time. You have a high chance of getting kicked out if you try this, though. I usually showed up at low-traffic times so I wasn't realistically stealing courts from players that wanted to reserve a time on them.
15. Look for AS MANY opportunities to play as possible. Ask all of your friends to hit with them so you get experience not only playing tennis but also learning how different people play. Look for student/member opportunities like the free court time in the above point. Play tons of hours per day with friends and family. I can't tell you how many players I blew past on my high school and college team ladder that talked about their "advanced tennis camps" that they paid $$$$ to attend while I just focused on high volume and VERY PURPOSEFUL practices for free with my friends for free at my local park. During high school, our coach was very smart and a no-B.S. guy. He said he would stay with anyone after practice to work on anything and I capitalized on these free 1-on-1 lessons.
16. Notice how I said "purposeful" in the above point. Practice with your friends and during lessons WITH A PURPOSE. With no goal, you are not giving your brain a reinforcement pathway for you to get rewards from as you inch toward your goal. Show up to practices thinking "I want to practice serve-and-volleys today so that I can scare pushers better" or whatever you want.
17. Hit up. You want several feet of net clearance on your groundstrokes. Your racquet head speed and spin will bring the ball down quickly and let you have power too. This clearance is to make sure you don't hit balls into the net and give your opponents free points. A long baseline miss is better than a wide alley miss, which is better than hitting into the net. Unless you are 8 feet tall, you cannot hit down on a serve or groundstrokes. Think of hitting up all the time (especially on serves) and letting your spin and physics bring the ball down.
18. Practice unexpected shots if you have extra time. For example, I would always practice viciously-dipping cross-court passing shots during practices in high school because I could mess them up with no consequence and more importantly, opponents during matches would shift to the side of the net toward which they hit their approach shot (as they should) only to get passed by a cross-court shot that they did not expect and that I could land 95% of the time. A well-known trick to easily win beginner and intermediate-level matches is to pound your opponent's backhand because it is the weaker shot of the two groundstrokes for most people. As soon as I learned this in high school, I dedicated all of my groundstroke practice towards my backhand until it got better than my forehand. I would go into matches just unloading on my righty opponents' ad-side and they would feel so uncomfortable because they didn't get to hit any forehands. This is trick #13: make your opponent suffer. I would also practice running back while getting lobbed at the net so it became an easy recovery during matches.
19. Don't serve too much during practice. Focus on technique and consistency more than anything else during serving practice. The serve motion is bad for your shoulder so if you crank out 300 hard serves at practice, you will go home with an injury.
20. If you are suddenly playing really badly at practice, it might be because you ran out of energy. I can't even count how many times I went to practice for 4 hours with my friends and absolutely beasted the first two hours and then ran out of energy which made me get sloppy and play bad and leave annoyed and confused why I suddenly got worse. Remember, contrary to popular belief, tennis requires a lot of fitness and you probably can't be swinging, moving, and setting up at full intensity for 4 hours straight unless you are fit.
21. The sun is powerful. Learn how to hit consistent blind serves if you have to serve right into the sun during a match. If I had to serve right into the sun, I would do both serves at 50% power and close my eyes at contact so I didn't start the point with a bunch of bright moving shapes clouding my vision. Your serve should be so developed that you can hit alright-decent serves with your eyes closed for the second half of the motion. Not only that, the sun can give you sunburn. Dermatologists recommend sunscreen even if you aren't going outside because the UV rays that the sun gives off will happily pass through light fabrics and translucent materials and burn your skin with non-ionizing radiation. You are at a greater risk of cancer and aging if your cells replace themselves a lot, so be smart and show up with a hat, sunscreen, lip sunscreen/balm, appropriate clothing, and water. You may look like a weenie when your friends make fun of you for being "over prepared," but you will be healthier.
22. Make friends and "collect" hitting partners. In high school, many of my tennis friends were not as motivated and would only want to play once or twice a week with me during the school year so I would get around 4 to 5 friends on rotation so I would have a hitting partner each day. I would also try hard to make friends at matches and events, especially players that were way better than me, so that I could "collect" hitting partners. (That's quite a morbid word to use but I thought it fit the mood.) I would also seek out players that were way better than me so I could get practice against very good players and hard hitters. Most would say no, as expected, because they have nothing to really gain from a practice with a much worse player, but some friendlier ones said yes and after a year or so, I would catch up to their level and be their normal hitting partner.
23. Have fun. Tennis is a really fun sport and there is a 99.999% chance that you will not go pro so you might as well have fun. The only reason why I was willing to put in so many training hours was because I thought it was very fun and I loved to get into competitive situations with my friends.
24. Analyze opponents before matches and yourself after matches. My high school coach was a very smart guy and always had the scoop on each player that the team would face and he would tell us in advance so we could prepare. This helped out a lot because for example, I would practice net rushing if I knew I had to play a pusher in a few days. I would also ask my coach, teammates, parents, and friends for anything wrong that they noticed in my matches. I would then practice my shortcomings in practice the next day. This is pretty much common sense in every sport. I once went into a match with no plan because I didn't study my opponent. He was hitting winners off of my groundstrokes with his insanely powerful forehand and I was down 4-6, 1-5 (match point). I noticed that he always missed backhands so I started pounding the ad-side of the court (this is the day that I began using ad-side backhand pounding strategy). I came back for 4-6, 7-5, 6-0 because he missed 90% of his backhands and I completely deprived him of any forehands.
25. Avoid hitting against walls unless you are doing volleys or something innocuous. Walls rebound the ball much faster than a human and you will shorten your groundstrokes and ruin them if you hit against walls too much. You are better off just doing shadow points and swings or doing drop-and-hit to yourself on a court.
26. Feed off of jeers and harassment. You can just ignore the crowd if you want to but I always took it as a compliment. In high school, my state had this very talented team that was known for harassing opponents during home games. I had to play-up against a top-10 player while his teammates shouted insults at me. The ENTIRE time I just thought, "They hate me because I am not losing easily." My match ended up in a draw because some crazy wind storm happened at the beginning of the third set and we had to evacuate the courts. lol. It was so satisfying to watch a bunch of immature teenagers get mad at me because I wasn't losing quickly enough.
27. Be careful before matches so you don't get injured. I was a clumsy person and I had a couple situations where I would trip and hyperextend my knee or get my finger caught in a fence door and rip the flesh open right before practice or a match like a complete idiot.
28. "I can do this all day." This is similar to making the opponent suffer. You want to bring this attitude of "I can do this all day" to matches. It will demoralize your opponent as they watch you hype yourself up in a great mood during changeovers while they sit and rest with their head down thinking, "I can't keep up."
29. Eat your losses. You will have matches that you are guaranteed to lose. Just play your best and if you lose, you lose. Be nice and have fun.
30. If you play a really bad player, practice your worst shot selection on him. During practices I liked to play against players that were several spots lower than me on the lineup and only go to the net. I could serve them two bagels on a platter in 30 minutes with my groundstrokes, but practice has no consequences if you lose so I would just practice my net play on every point. Do not be so cocky that you pass up opportunities to practice against worse players. It is better than no practice at all. Modify your goals for a worse player so that you still benefit.

Good luck.

My playstyle and background for context:

Male

5.0 NTRP and starter on decent D3 College Team

Moderate power high percentage serves.

Powerful groundstrokes with heavy spin.

Confident at net if I need to be, but it's not my first choice unless my opponent sets me up or I am playing a pusher.

Relentless intensity and speed with the intention of pounding the opponent's ad-side and making them feel like hitting a winner is impossible.

A bunch of random niche shots like the cross court dip passing shot that I can consistently land.

Really bad at overheads. lol.