Do not wait for enemies to get out of cover. Instead, repeatedly shoot at the same spot on their cover and it will eventually break down. Boxes will break down completely, concrete will chip away, and cars will explode. Note: The same happens to your own cover; keep moving from cover to cover to avoid enemy fire. The benefit of this is that it may open opportunities to take down enemies that were behind cover. They will usually move soon after being exposed, but you will still have time to shoot them. When dealing with snipers, move from cover before they shoot. If no spipers are around, change cover while under enemy fire will cost less health than being directly shot at because your enemies aim slower when you move.