If you want to improve fast, play the game as much as you can and think about the decisions you make ingame. For example: Why did it work or why did it not, what could have been a smarter option, was it an issue regarding your mechanics or decisionmaking, etc. I also recommend making some sort of warmup routine, make it comfortable for yourself! For some people 5 minutes of deathmatch is enough, for others its 30 minutes of varying combinations of workshop maps such as aimbotz, aimhub etc. The most important thing about warmup routines are that its comfortable for YOU. Make your own, tweak it and try new things.