If you or stuck on badguys,here are a few tips.
1.Use wraith's sniping ability.It will help maintain stealth.
2.Up the carrying skills so u can carry alot of ammo,sniper ammo,air strike,medipacks,and grenades.
3.Maintain stealth[dont waste ammo,snipe alot, and dont attack from long distances giving your location away]
4. In heavy enemy territory field of fire & fire at will help.(hold x and select field of fire or fire at will)