Seeing as most of the active members here have MW2, I figured I could help some people trying to get some of the more difficult perks or make easy perks simple.
Cold-Blooded: Make a class with a light machine gun of your choice (minus the Steyr AUG HBAR) and a rocket launcher (I suggest using the Stinger; it has two rockets and is extremely powerful). Whenever there is enemy air support, switch to your anti-air class and shoot it down. If someone destroys it with an LMG, unload on it. Each bullet that hits the destroyed aircraft (unless it was exploded) will count as a kill towards Cold-Blooded Pro.
Marathon and Lightweight: These are fairly time consuming and take up two good perk slots (Sleight of Hand, Stopping Power, Scavenger). Combine them and run around with a handgun or machine pistol.
Sit-Rep: Not worth it.
Scavenger: Easy to get. However, once you get Scavenger Pro, you always start with full ammo so you can't get anymore. When you see a blue backpack, spam flashbangs or semtexes to get Scavenger Pro V(+).
Last Stand: Do not use the Desert Eagle. It has been made worthless in this game. Use the magnum and Stopping Power.
Commando: Don't run at people, camp!
Ninja and Scrambler: Use a P90 and Stopping Power. Spray and pray or camp near an objective.
Danger Close: Combine with Scavenger and spam grenades.
Hardline: Use on powerful guns (FAL, TAR-21, UMP .45, lmgs). Every two kills in row add one to the killstreak count, plus they stack. You do not have to use UAV, Care Package, etc.
Steady Aim: Easy to get, but don't use it when you're trying to get a holographic sight. That's just pointless. Permalink
I agree that trying to get Sit-Rep pro is not worth it. But a super easy way to get the sprinting pro perks is get in a wasteland match, and sprint around the edge of the map. Using Marathon Pro and Lightweight pro is really helpful in gametypes like CTF and domination! Permalink