Try and always use a clean mousemat. If your Cusor doesn't want to move uniformly when you move mouse (ball mouse only) it may well just need cleaning.

Holding the mouse upside down follow the directions on the retaining plate. In this case rotate, some are pulled down. Put your free hand over the ball and turn it upright again, the ball and retaining plate should now be in one hand and the mouse in the other.
	At this point you can if you want wash your ball, they don't usually need it.  Now turning the mouse back on to it's back, look in. You should see a pair of rollers the same and single spring loaded one. The pair are what convert your movements into inputs. These rollers can be plastic or metallic, They should be smooth, but you  most likely find build ups of muck (sweat, skin, etc)
Using a cheap ball point pen top (or a blunt edged peice of plastic) drag it across, rotating as you go) the roller, until all the muck is off. Don't forget to vacuum/blow or shake out the bits.