Find the crashed plane.

1. You can get under the lowest part of the wing. There is a hole above you that lets you shoot at the cliff without being seen. You can also watch out towards the other side of the map from under here.

2. Climb the lower wing by the aelerons (XP?). Run up to the highest point and jump onto the 2 small pipes above the main cave entrance. Once on these pipes, turn right and look at the ledge there with 1 small bush on it. Get on the right edge of the pipe nearest to that ledge. Jump directly at the bush. Snipe from there. This spot overlooks much of the map and is rarely used.

Note that the rock there sort of blocks your jump, that is why you must stay on the edge of the pipes and jump to the bush. If you jump to the nearer side of the ledge, the wall will affect your jump and you will just fall below.