generalized reinforcement learning/targeted practice:
1. Identify what you're weak in, eg. streams, jumps, double+slider+jump, missing tactics like skewering queen to rook with the bishop (doesn't just apply to osu!)
2. Train yo brain to do that easier
The reason for this is if you can afk clear some portion/recognize something, you can fall back on habit while using your mAPM somewhere else
3. Repeat!
That's really it! Back when I played an instrument, I would practice the hard part... practice the transition into the hard part... and then practice the transition out of the hard part. Given that any beatmap contains a finite number of the things... mastering each portion will make you a master of the whole.
Osu and any other skill (I'd imagine) is like riding a bike. You need to incrementally build key habits until thinking is not required. But this is coming from a guy with 15h playtime. Take it with a grain of salt poggers
edit* oh I should mention you learn through building connections in your brain and using them repeatedly. I suggest something like 15-30 minutes practice + some break (let the short term connections decay, a few minutes to a couple hours) + repeat to rebuild your gains