Mw2 staying alive tips?

Hey guys i've been playing mw2 for a few days now and I really love it. My question for multiplayer is that I see people getting harriers and pavelows left and right every game while my average highest killstreak for a match is about 5 - 6 then I usually get blasted out of nowhere. Sure I get lucky sometimes and get the harrier killstreak but it comes very rarely. Any tips on staying alive to earn killstreaks more frequently?