One tip to improve your aim in PC gaming: 
If your mouse speed is high, reduce it.

Many PC users and gamers have a habit of having a high mouse movement speed.  This is either caused by a high DPI setting on the mouse or a high sensitivity setting in-game.  An eDPI is calculated by your DPI multiplied by in-game sensitivity.

I was wondering why my performance was getting worse as I got a gaming mouse.   A friend calculated my eDPI to be 15000 (3-4 as much as many good players), I was shocked, but now I understood what was behind my losing streak.  I cut down to 6000 and I’m weaning down.

It’s a hard transition to make.  It is fun to be able to move around your mouse quickly across the screen with just an effortless nudge of the thumb.  But this causes games to over-react to your movements.  Tracking a moving enemy requires much less mouse movement than turning around.  However, this means that moving the mouse the teeniest ant-sized amount extra than you had intended results in your mouse being moved too far.  With high eDPI, your intended movement of the reticle from the enemy’s arm to their head might accidentally move your reticle above their head (and you miss).

Switching to arm-aiming instead of wrist-aiming takes work, but it makes aiming far more precise.  Yes, you will have to move your arm in a large motion to turn around.  However, when you are tracking an enemy with a reticle, you’ll be more accurate.  Some games and some characters (such as Winston in Overwatch) don’t need to aim and can benefit from faster turning speed.  I set my eDPI a bit higher in those cases, but not too high because I’m still trying to learn how to arm-aim.