How To Aim Better At FPS Games.

It depends on the game of course but here are some rules that you may find helpful:

1. Don't spray, make every bullet count.
   For shotguns and sniper rifles it means that must be confident that you are going to hit your enemy when you shoot. At first it might become even harder to kill someone but it's a proper way to improve your aim.
   2. For assault rifles it means that (again, depends on the game) you should shoot in short bursts making a tiny half-second breaks to decrease the spread.
   

   

   
   3. A good mouse and mouse sensitivity that suits you. I think majority (debatable I guess...) of professional gamers use rather low mouse sensitivity. They use the whole arm and the whole mouse carpet to turn 180 and use their wrist for precise movement. It is also important to have enough space to move your mouse. I feel extremely uncomfortable when there is something fragile on the same table where I sit...
   
   4. Turn off mouse acceleration. Everywhere: in mouse drivers, in OS settings, in the game. Most people agree that it helps but there are a few guys who like to have it on.
   
   
   5. Turn off vertical synchronization, tune your network settings. For source games cl_interp, cl_updaterate, cl_cmdrate etc can make a difference.