>>373860561
To add on to what >>373862672 said
Virtual stock if you have shaky noodle arms until you've built up the muscle memory. Turn it off when you feel comfortable.
On long range push maps or when using single shot weapons, aim a bit in front and let the enemy walk into your sights rather than chasing them with your sights.
Avoid standing stationary unless most of your body is covered up by something, it's a death sentence on obvious corners.
Throw grenades with more accuracy and distance control by pushing them like a shotput throw.
Think about unusual angles, the less the enemy expects you the longer it will take them to shoot back. Even better when you let a few pass then gun them down from behind.

Play with the guns you enjoy, in the gamemodes you enjoy and on the maps you enjoy most of all.