The lights are on
You are reading this guide because this is the first time you've played a shooter, or because you've heard about the popularity of Modern Warfare 2, or maybe you just suck. So now that I got that out of the way, I want to tell you this:
Everyone needs to start somewhere, and It's OK if you need to start with a guide. Here I'll explain to you were to start, and what weapons you should use (according to you, i'm not gonna go "ACR PWNS, DONT NEWB TEWB!!!!!").
In order to find what you are good at, you need to experiment. Use each of the starting classes, for they are real balanced, and have good weapons.I divided up each main section into what your primary is, because your primary basically decides what type of game you need to play on the battlefield.
The Assault Rifle is going to be your best friend, and is made for all-purpose warfare. AR's (Assault Rifles) are best at medium range, but can sometimes be used as suppressing fire at long range. Some AR's are good at close range, but it's often better to switch to your machine pistol, pistol, or shotgun if you have one on you. Assault Rifles are very accurate, so try and minimize spraying (shooting from the hip)
The Sub Machine Gun (SMG) class is specialized for close range, and often have really fast fire rates (I could, no should just say always). These are extremely light guns, and are great for running around corners, and spraying (shooting from the hip) at enemies.
The light machine gun is great for beginners, it's powerful, inaccurate, and has huge clips. Light machine guns in Modern Warfare 2 is the best way to get better at first person shooters in general. The LMG (light machine gun) takes forever to reload, so make sure you do so every time you have a moment to breathe.
Okay, don't get all excited. just because I said sniper rifle, doesn't mean I'm about to make you all PWNzer. The sniper rifles in Modern Warfare 2 can range from user friendly, to Major League Gaming level. The best way to start on sniper rifles is learning the two types of snipers. There are bolt action (high power, long reload times), and there are cartridge fed (medium power, shorter reload times). Most likely you should start with sniper rifles that are cartridge fed (EBR, Barrett)
This is the newest weapon to FPS, and it's pretty different. It has it's own class, but there's only one of them. Bullets stop on it, or ricochet somewhere else. It slows you down, and about nothing stops it. When you're holding it, your back is open and you can't fire a gun. But when it is unequipped, you are able to wield your secondary (or any primary gun you pick up off the floor), and bullets ricochet off your back.
Now try all of this, and whatever works, stick with it. try different attachment combination's and perk setups. Your secondary (if you're not using one-man army) can be a life saver. uses could range from a fail safe when your primary is out, or something to use for close range, and some others you could use to take out enemy kill streaks that are keeping you from spawning. Unlike most shooters, MW2 made shotguns a secondary weapon, and this opens up the possibility for sniper/shotties combination's.