How to improve aim?

Skilled players typically use lower sensitivity for fine aim control. I don't know if you play on PC or console, but regardless, the only real tip is to just keep playing and practice, try to get into as many gunfights as you can be in, don't shirk from a fight. It'll help get in the practice you need.

If you're new to shooters, getting to lvl 50 or so on your account isn't any meaningful experience.

The really good FPS players have been playing for 10+ years. So don't beat yourself up for not being as good as them if you just started playing.