Use easy guns like the ACR 6.8, run Blindeye and Assassin to avoid air support, sentries, and the UAV. And I suggest playing the maps offline or in a private match just to get more familiar with them. I dread not having Blind Eye and Assassin cause even if you don't camp the constant UAV spam alone is enough to really screw up a match for you. Plus if you don't run Blind Eye and you just happen to be doing well helicopters will target you as a high threat. It's been that way since COD4. I tested it out myself I jumped into a match using my Sleight of Hand class. I was doing really well then the helicopters came out and just started smoking me, lost an AC-130, got spawn killed about 3 times in a row, then when I've been smacked around enough they leave me alone with about 5 extra deaths. Broke my personal mantra so I got nobody to blame but myself for that one. Personal Mantra: If you can't be humble in the presence of an Attack Chopper you better at least be sneaky.
I just prestiged so I decided to give my MK14 a break and used the M16. Wow. I was surprised at how many one burst kills I could get with it. And for once when I won I wasn't catching flak in the lobby. I might gold this on this prestige :)