Slip and slide:
When you are running and suddenly get fired upon, quickly tap the Left Analog-stick. You will slide along the ground. If you are running and click and hold the Left Analog-stick, you will do a sort of belly flop and slide on your stomach.
If you are carrying a large automatic weapon, the controls will feel sluggish because of the weight of the gun. However, if you switch to a hand held gun, the controls will be more responsive.
Successfully complete the game to unlock the Warfighter difficulty setting.
Walls and barriers:
You cannot hide behind walls or barriers in first person view unless you plan on staying at that location for awhile. Unlike third person view where you can just tap Triangle to automatically hide, you must hold Triangle in first person view to hide. Press Up to look over a barrier or to open fire. Press Left or Right (depending on how you are positioned) to look out.