in order of practicality
#1 play more
lock in as per Seinfeld's advice. Are you already playing the amount of hours you can muster without suffering in terms of grades/social life/etc? Think of how to use your time more efficiently. 30 minutes of scrims is worth a lot more than 30 minutes of pubbing as an example
#2 rocketjump on a variety of maps
different jumps will force you to be consistent with both precise mouse movement and flicks
#3 aim trainer games
They're overrated and you need to do it right. variety in flicks, tracking, scenarios that require full 360 movement, horizontal and vertical, etc. Rocketjumping takes less effort because you just join a server and go
#4 different settings, mouse accel, etc
I do not recommend relearning your muscle memory. But I'll post it just to have it listed. That new crosshair or HUD wont make the difference either