Ok so the basic advice that every gives all the time for improvement is "play more". However you are asking for the science so ill give you a brief idea of what differentiates good players from bad ones from a scientific perspective. The key difference is that good players have both a physical difference in their hands and in their brains.
For the brain, you build up a thicker layer on myelin for neurons used to play osu every time you play the game. For the body, your muscle fibers adapt to the strain put on them and grow stronger. Both of these processes require playing the game as well as resting and recovering.
The best way to improve is to play more but to also to maximize the recovery process as well where myelin is formed and muscles grow. This means that things that boost health like exercise, good nutrition and good sleep all make a difference to become better faster.
If you want more details check out:
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This video on how the brain learns new skills and habits
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This video on how exercise has a massive effect on the brain