Modern Warfare 2 is th-DAKKA DAKKAaaaaaargh! ...the kind of game in which you die suddenly, and a lot.
It's an ineviGRAAAAARGH!tibility of contemporary weapons technology: things kill people fast. If you haven't spotted your assailant when he opens fire, it's foom... OOM! Gleurg - bad news.
In some cases, unfortunately, you'll die to weapons you haven't yet unlocked, such as the dual-wielded BANGBANG My precious face! shotguns with their improbable range. But this guide won't assume you have any of those: a lot of powerful stuff is unlocked surprisingly early on, and I'll tell you snick - blurgh exactly when you get them.
Early on, don't fret too much about getting back to the fight when you die. Unless you clearly saw what happened and why, take a second or two to watch the KillCam. The best players have found fiendish spots to lurk in, and some of your most bloody sprees will come from simply getting there before them next time.
Similarly, bear in mind you can always grab the weapon of any fallen soldier, and when you're just starting out this is almost always better than yours. In an average game, you're bound to find a few dual shotguns or high-level assault rifles with twin attachments already fitted.
1. STOPPING POWER
Stopping. Power. Stopping Power Stopping Power, Stopping Power. It's a perk available from the start, and it's all any hot-blooded soldier will ever want in that slot. That's because Stopping Power increases your bullet damage, and nothing really trumps that. Every time you lose a head-to-head firing match without Stopping Power, it's because you didn't have Stopping Power. Get Stopping Power. Stopping Power.
2. GO COMMANDO
Commando basically lets you win every very close range encounter with someone who doesn't have Commando. It extends the range of your insta-kill knife attack so that you effectively teleport the last few metres to your target. Provided you hit the key fast enough, there's nothing they can do: you're literally faster than a speeding bullet, and the blow kills anyone regardless of gear. So bind your knife key to something easily accessible, like Alt.
3. SCAR AND TAR
Despite its might in other games, and in reality, the M4 you start with is depressingly feeble. At level 8 you'll unlock the SCAR-H, and this will be your best friend for 12 levels: full damage, great accuracy. At 20 you earn the TAR-21, which on paper looks worse: same damage, half the accuracy. But its rate of fire is ferocious, and the first shot of a burst is still precise. This is your mainstay until the M16 at level 40.
4. SHUT UP
Kill 75 people with a gun and you'll earn a Silencer for it. Not many people bother with them because they reduce range, but in practice that's almost never a problem. The plus side is twofold: firing normally lights you up as a blip on enemy's minimaps, and silencers stop that. Secondly, they actually do work: you'd be surprised how often your gunshot and muzzle flash are what get you killed by an unseen opponent.
5. TAKE CARE. PACKAGES
Don't forget to fiddle with your killstreaks, my grandma used to say. You can only have three enabled at a time, and for some kill streak amounts there's a choice of rewards. Choose the Care Package reward for 4 kills: a Care Package is an airdrop crate that can contain any other killstreak reward short of a nuclear bomb. That includes the ridiculous AC-130 and Stealth Bomber attacks. If an enemy calls one in, you can also steal theirs.