Aim for the head in such a way that the kickback of the firing weapon lifts the next bullets into their head.
keep your crosshairs in the center of the screen at all times.
the little x that lets you know where your weapon is aiming.
youll get used to it. It is all visual. sounds are misleading, just search for movement and keep moving.
First of all: Get an Xbox, PS3 is horrible. (jk, don't worry.) Seriously though, you could start the game off on easy, and as you start to play the game it teaches you the controls. When you can learn each control fine then you can progress through the game.
I doubt any of that made sense, but, whatever.
Online as in, fighting real people? I wouldn't worry about it, usually its harder to compete against real human beings rather than a computer generated object. Some people are also more skilled in playing certain games on a computer rather than a hand held device, xbox/ps3, etc.
Plug your mouse and keyboard into your PS3.
Practice. I was sponsored to play CoD. Just takes lots of time and practice.
My first cod game was CoD:3 I'm not sure if I ever got a kill online. But by the end of CoD4 I played comp. There is no real shortcut.
alot of times on pc people are hacking (cheating) thats why I play on wbox it is way better. SugaryPheonix62 is my gamertag
Once you have some base accuracy behind you start playing aggressive it will make your reactions faster.
LOL Just concentrate use manual weapons to start with and play as often as you can,
Keep playing ,seriously