Sniping is basic, very useful tactic.

Have 2 classes:
1 - Claymores
M4A1 + Silencer
One Man Army Bag
Claymore
Stun Grenades
One Man Army
Cold Blooded Pro
Ninja Pro

2 - Sniper
Barret .50 Cal + FMJ
One Man Army Bag
Claymore
Smoke Grenade
One Man Army
Cold Blooded Pro
Steady Aim Pro

Using these two classes, spawning with the "Claymores" class allows you to get to your sniping area and quickly setting up with two claymores. Having OMA on the second sniper class is optional, but it can really help out.

NOTE: Try to use claymores to secure as many entrances as possible. If there is only one entrance, try to put 2 claymores in seperate locations for extra security.