make sure to turn off 'enhanced pointer precision'. take a look at this vid :
https://www.youtube.com/watch?v=lXnzLgakST8
it's actually quite funny, a little vulgar, but this guys is a gaming God and knows his stuff. It's mostly about setting up a gaming mouse with higher DPI settings (this is really important for FPS gaming - so it's worth considering getting a gaming mouse, but as Ralston pointed out, maybe not required just yet), but you can apply some of the recommendations to a traditional/standard laser mouse.
Getting used to the higher sensitivity/DPI settings will serve you well, specially if playing First person shooters. When you change the sensitivity/DPI naturally it feels like madness, and you wonder how you can get used to it. But if you follow some of the basic settings in the video, asides from the mouse specific high DPI settings, and give it a day or two, you will be grateful for taking the pain

Your movement in-game will improve.