I be stealthy most of the time. Use silencers and perks that make you stay hidden from UAVs/Spyplanes. IE: Ghost, Assassin, Cold Blooded. Don't keep camping in one spot unless you have your teamates to back you up so you don't get flanked, otherwise you'll eventually get taken out. Rotate around the map to keep your enemies occupied with finding you in that one spot you killed them in before.