In multiplayer select the Summit map.

In the map there's a circular building like platform. Walk right up against the wall and force the left analog stick left while walking.

There will be a walkway, go onto it.

Note: don't back up too far or you'll fall off the ciff.

You'll get a great range to fire from on the left, but on the right you get a narrow view.

No one can see you while you are hiding here,it works great for assault rifles and it's very easy to pick off enemies to get killstreaks.

When you have the SAM turret, it's a bad idea though because while you're capturing it, it leaves you totally exposed to enemy gunfire.