Switch to single-fire if you are in a safe location and are shooting enemy from far away. When you are in close quaters do not crouch but spray it like an assault weapon. Otherwise keep it on auto mode and alternate between single burst shots or automatic shooting from a crouch position. My preference is to use more burst/single shots on auto mode because it is faster since I do not need to crouch and hence makes me safer overall. I crouch and auto shoot when I feel like I am safe to spend a bit of extra time auto shooting. Also, sometimes avoiding enemies is the best strategy. If you see someone across the map and you do not have time to single switch and fire I suggest to fire a few rounds from auto mode, if you do not kill the guy just run away because otherwise you give away your location.