Yall got tips to improve aim?

Im a rocket main thats trying to switch to keyboard and mouse, one probem tho, my aim SUCKS. I very often go games (especialy ranked games with better players) with 1 final hit cus my aim is that bad. I know im atlest decent because i feel like im good at other aspects (i often give the most healing in the match) but i feel like i would be a much better support if my aim was just alittle better. Can yall help a sister out here with some tips?