Hi, I'm that player you see in the other court ;-)
What a lot of intermediate players do, is playing with little to no control. They smash on balls they probably shouldn't do, they play their groundstrokes too fast and with too much slice.
They try to volley with a lot of slice like the pro's on youtube, etc.
Nothing wrong with the above, as long as you are having fun.
If you want to move towards intermediate+/low advanced:
1. Take classes to work on technique (basket of balls) and tactics (there are some effective tactics that work on all levels that you should know)
2. Use a suitable racket for your level. Use something with a big sweet spot and not too (head)heavy. It may be an advanced racket, but just not too demanding. E.g. Siux Diablo Pro is advanced but still good for intermediates. Same for the Wilson Endure Pro, etc.
3. Play a lot of friendly matches and try to apply what you have learned during the classes.
4. If you find a partner where you feel it clicks, try to play slightly more matches with him.
5. Try to play some official tournaments from your federation with the partner where it clicks (tournament is not the same as a friendly playtomic). I know players that are quite ok in a friendly but are worse when it's actually for real.
6. When you feel that you are getting more confident in your game (you start to easily beat your usual opponents), try to play a match against slightly better players. They will expose your weaknesses and get you out of your comfort zone.
7. I know I said to try to find a fixed partner. But keep challenging yourself by playing with strangers, it will make you more resilient (e.g. join americano's, king of the court, etc.)
8. Video yourself.
I am e.g. advanced and I'm testing myself against the better players of my country since 3 months. I can play with them, but they expose me so much.
Things I got away with 3 months ago... Not the case anymore today.
So I'm even more focused now during matches and I feel I'm getting better again.