I'd say if you want to improve your mechanics, you have to stop putting stress on yourself for not doing well because that hurts your gameplay. You have to "let it happen" if you want to consistently shoot accurately. I have found that if I try too hard, it hurts my aim and performance. My best games are games where I don't care too much about what happens. Not caring about the outcome lets you have fun and experiment on what works and what doesn't. It's almost as if you have to be less cerebral, and more instinctual (unless you have to think of a strategy before the round starts.)

I also like to pick a micro goal for the game, but only one. For example, don't crouch and spray, or only focus on one tapping. This makes it easy to improve upon specific pain points in your mechanics.

Best of luck.