6. GO PRO
There's a 'pro' version of every perk, with a major extra benefit, earned by completing the fourth challenge for that perk. Stab 20 people using Commando and it becomes Commando Pro, which renders you completely immune to fall damage. Scavenger Pro gives you higher ammo capacity, Cold Blooded Pro removes the big red name above your head on enemy screens, and Stopping Power Pro lets you destroy air support more easily.
7. THE IMMORTAL SNIPER
Like killing but don't like dying? Snipe. Getting one-shot sniper kills unlocks some extremely effective camo suits, and one of the best rifles to do it with is yours by default: the Barrett 50 cal. Fit it with a silencer, and at level 11 take Tactical Insertion. It's a beacon you can hide in the room you snipe from, and when someone finally backstabs you, you'll respawn behind them. At 31, replace that with Claymore mines to boobytrap the route instead.
8. EXPLODE LESS
Enjoy getting obliterated by randomly flung grenades? Me too! That's why neither of us should take Blast Shield, unlocked at level 19. It ruins the fun by cutting explosion damage sufficiently that you'd have to virtually sit on a grenade for it to kill you from full health. It also means grenade-launcher wielding enemies have to use - spit - skill rather than splash damage to take you out, utterly defeating the point of the game.
9. RPG HERO
How often do you use your secondary weapon? Unless you've unlocked something ridiculous for that slot such as the twin shotguns, not much. So do your team a favour and take a rocket launcher in that slot. With the aforementioned Stopping Power Pro, most enemy air support can be taken out in one or two shots, saving dozens of lives. The chance doesn't come up much, but when it does, you're a goddamn hero.
10. THE GHOST
I mentioned Stopping Power was a must for hot-blooded soldiers. The cold-blooded ones should take Cold Blooded, a level 25 perk that makes you invisible to enemy UAV, turrets and - this is the kicker - air support. That eliminates the game's most frustrating deaths, and gives you time to line up anti-air shots. Blow up 40 aircraft to get Cold Blooded Pro, which stops enemy crosshairs turning red when they point at you, and hides your nametag from them.
11. DRAWN AND HEADQUARTERED
In Headquarters, players rush to a randomly selected capture point as soon as it pops up. In Modern Warfare 2's Headquarters, they shouldn't. The capture point doesn't unlock for a while after it's announced, so approach slowly, stick together and shoot enemies in the back as they heedlessly sprint to it. As soon as it's yours, retreat a little: the capture room itself is always a tactical nightmare, and you only need to keep it in sight.
12. WINNING WITH GRACE
In Domination, you win by controlling the majority of three capture points. If you only have one, obviously you need to attack. But when you have two, resist the temptation to rush for the third: it's much easier to defend what you have. If you have two then lose one, nab the enemy's other point instead of taking yours back: most of them will be at the one they just captured. If you have all three, find a safe spot, bring up chat and type the following: lol.