Put your crosshairs over an enemy and click.
Play on a console so its easy mode.
I've been called a hacker in every MW3 game I played today. I just use the Mk 14 (suppressor and plain red dot) and the SMAW. I start every life running around with the SMAW, trying to kill people at any range with it. It's difficult, but rewarding, and someday I'll get the gold SMAW and it'll all be worthwhile.
Then I just use the Mk 14 and go nuts. I never sit still for more than 10 seconds, just keep moving, watch where enemies go and try to shoot through things to hit them. I imagine my uncanny ability to do this is what gets me accused of being a hacker. The real trick is to be faster than the other guy. This is especially important in close quarters, practice knifing, it should be second nature. Overtime, you'll build muscle memory and you'll become much faster than everyone else.
What's always worked for me is these 2 simple rules:
1. Don't die
2. SMAW others
First of all, stop measuring your performance with your KDR.I always suck at FPS games online. How do you get good? my K/D is .584 in Call of duty mw3 and .483 in BF3
Does BF3 even have 1:1 mouse sensitivity yet? I played for probably less than thirty seconds and had to stop because of negative acceleration.Setting your mouse correctly and building muscle memory are both important parts of getting good at an FPS.
First of all, stop measuring your performance with your KDR.
seriously ^this.
It's been said, just need to "know" the maps and not camp. I recommend playing with a burst fire/single shot gun to improve your accuracy.
It forces you to accurately hit your first shots. After that, your muscles will apply your aim to fully autos.
Also, when using full autos, burst fire at longer range to improve accuracy.
Learn when to run and when to not run. For instance, try not to run around corners, because your gun will not be ready but theirs will be.