Perfect 180 turns and aiming

Beyond setting your mouse sensitivity high, disabling the "enhance mouse precision" option on the Windows control panel (you may need to go into the Windows panel, even if your mouse has it's own) can help greatly for shooters. What it does is essentially reduce the pointer sensitivity the slower you move the mouse, or conversely speed it up the faster the mouse moves. With that done away with, when you move the mouse an inch in whatever direction at whatever speed, you will always turn the same amount.

The downside of this is that unless you have a mouse with high DPI, you may not be able to have both the sensitivity as high as you like and have your cursor move smoothly (it may skip pixels)