When I got my PC, I just played. I don't have OW on PC yet but I was playing a lot of fps games. I struggled, but I started to realise that I was getting it and it was getting easier
a comfortable gaming mouse is really important, try to spend some time in the practice range playing people like widow and soldier so get used to crosshair placement
Just start in quick play and adjust as you play.
Setting for mouse sense
Crosshair
If the screen brightness is enough.
Get a feel for the heroes you already played in the Xbox Version. This a must!
You should be pretty set after that. It’s not a huge difference, but being more precise is gonna be key when playing on pc.