I would start off slow... learn the maps because so many people will have a jump start on ya. Secondly, I would camp a little.
I know I know... camping for noobs. Honestly, this is the first COD game that I camp in at all. It feels like you get killed too easy so don't give up right away if you seem to die more than usual.
Playing demolition game type gives you a ton of points so once that is unlocked for you i would hit up that game type. If you're not sure what that is... it's sort of like SND w/ spawns and two bomb sites.
Lastly, don't try and be a hero with your kill streak rewards. Care packages, predator missles and harriers can give you some easy kills.
I found this to have some helpful information in it:
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Feel free to add me: PSN is rjive