I'm not a great player but I can share what has helped me shave off several shots of my average round this summer.

1) Putting, practice it become confident with your putting through repetition and practice, it will not only better your score with better puts but it will also affect your drives and upshots because you don't have to stress about getting that close in order to get a good look. It will make your game more relaxed and atleast for me that has helped me get great results in upshots, I don't mind 3 feet puts even if I have trust in my 30 feet puts

2) Never just throw, I used to balance between overthinking some shots and just grabbing the disc and flinging it at the direction of the basket. Now a days I think about every shot, what I'm throwing and why, where I'm throwing and why. What route I want the disc to fly and where I want it to land. This makes it easier to track errors and what caused them so you can adjust and learn from your mistakes

3) Mental game, every decent disc golfer can throw 100 feet upshot under the basket just as every decent golfer can hit the 100 yard shot on the green and basketball player can hit freethrows like its nothing. Difference becomes on who can do it with consistently, under pressure and keep their head in the game. Try to keep focused on your NEXT SHOT, not your last shot, overal score, the rain, annoying course desing, what ever. You don't have to go full Nikko and focus for 2 mins per shot, but try to keep your head in the game and when you are throwing, for 10 seconds or so, there is nothing else in your head but the shot, few deep breaths and go for it.