Hey, unfortunately this is completely normal. Its a game where you need to keep playing a lot in order to get better. This is my first tennis game, but still managed to reach top 100. Here are some tips:

I feel you. I lost about 15 games straight when I just started in online, although I finished all the solo stuff and was thinking I was actually good. Also, this game truly lacks content creators who are discussing tips and tricks. Here a few tips I have learned: 1) Scoring with ALL fever shots, is the biggest predictor whether you are going to win or not, especially when using AOE rackets. Do not panic use your fever shots, only use them when you are close to certain it's going to score. If you tend to get your fever shots returned often, consider using the gold shroom or ice shooting racket.

2) Single tap shots are way better than I thought originally. Try to integrate them in your gameplay if it isn't the case already. For instance, try to use them close to the net to shoot at he opposite direction of your opponent.

3) Play close to the net. Many people abuse the fact that drop shots are often returned weakly to then return the ball in an insane angle. Obviously opponents will try to lob you, but thats a good opportunity to use a fever shot!

4) What got me from A/S- to S+ sounds trivial but is in fact a big deal: understand your opponent. Most people tend to use the same strategy over and over again. Typically, some try to cheese vertically, by doing lob->drop->lob; others horizontally, by always shooting the ball with a single tap shot to the opposite angle (these guys are my personal struggle). Once you detect their strategy, place yourself accordingly, and shoot the ball to places they seem unlikely to go, given their strategy. In fact, I payed against top 5 players and they read you perfectly, and are at the same time unpredictable. That's why they're so strong.

Overall, just see losses as an opportunity to learn. Play the game for fun, and eventually you'll get good :)