Ranger Zoom
Press L to zoom with the sniper rifle to zoom in. Press in the Right Analog Stick to increase the zoom.
Quick Turret Disabling with Tech
Use the primary fire of your grenade launcher on an enemy turret to easily take it out quickly.
Telefragging
This can be done with any character as long as the person you are telefragging is on your own team. When you go up to revive someone, immediately after you revive them press Crouch to telefrag them. You will lose points.
Restore Vehicle Turbo
Exit a vehicle that has used up its turbo, then re enter it.