Unless it's misbehaving, you don't have to clean your mouse regularly. You're better off cleaning the mouse pad or the surface where it resides. Wash your mouse pad frequently; dirt and oil are quickly transferred from the mouse pad to the ball that controls your mouse's movement. If your cursor moves well in one direction, either vertically or horizontally, and erratically in the other, there's a good chance you've gummed up the works in your mouse.
First, shut down your PC and unplug your mouse. Now turn the mouse over and rotate the plastic ring on the bottom that holds the ball in place. Remove the ring and the ball. While you're at it, remove any crumbs or other particles from the ring and the ball. Inside, you'll see two plastic rollers set 90 degrees apart. One controls the mouse's horizontal movement and the other handles the vertical movement. Caked-on gunk on one or both of these rollers can cause a mouse to misbehave.
To clean the mouse, turn it right side up and lift it up so you can see inside. (This will keep dislodged dirt from falling into the mouse). Scrape any accumulated gunk from the plastic rollers using the end of a paper clip or similar implement. Make sure you rotate each roller to remove all the grime. A pair of tweezers is great for grabbing small bits of debris that may be trapped in odd corners. Then finish it all off with a quick blast of compressed air into the mouse's interior to dislodge stray particles. You should also wash the ball with mild soap and water. Reassemble your mouse and hook it back up to your PC. Turn your machine back on and your mouse should work fine.