How many times per day does your hand or someone else's hand touch your computer mouse?  When was the last time you cleaned your computer mouse?  You should clean the exterior of your computer mouse at least once a week, so my guess is that it has been too long.  Here are the steps to properly clean a computer mouse. 

photo courtesy of Dave Dugdale flickr.com/photos/davedugdale/5102302821/Daily Cleaning
For a quick daily clean, wipe your computer mouse with disinfecting wipes on all exterior surfaces.  Make sure your wipes are not too wet so no liquid gets inside the mouse.  Do not confuse disinfecting wipes with baby wipes that may remove dirt but only spread the germs around.  You may want to bring disinfecting wipes with you when you use a public computer, such as at a library or school, to disinfect the computer keyboard, mouse, and other computer parts you touch prior to using it.  Who knows the germs, dirt, viruses, and other nasty stuff that was deposited by the last people who touched it.  Also, who knows the last time it was cleaned or if it has ever been cleaned.

Interior Cleaning
If you have a computer mouse that has a ball on the bottom, it may get dirt buildup on occasion and cause it not to move as freely.  Before cleaning the inside of your mouse, disconnect the mouse from the computer or shut down the computer if using a wireless mouse.  To clean the interior of a ball computer mouse, twist the exterior ring holding the ball in place (typically counterclockwise but it could be clockwise depending on your mouse).  The ball should easily fall out of the mouse.  Wash the ball and ring using warm soapy water and let them dry.  

Inside your mouse are some rollers and maybe some small metal bars.  Using a soft cloth, wipe any debris off of these items.  You may use a slight amount of cleaning liquid if necessary, but make sure it is not going to drip inside the mouse.  Make sure to remove any debris that has fallen inside the mouse.  If your cloth cannot remove the debris, consider carefully using your fingernail to gently scrape the debris. 

Replace the ball and ring after the cleaning is complete.  Ensure that there is no moisture on or inside your mouse.  You can now plug your mouse back into your keyboard and turn on your computer.  Clean your mouse pad regularly so debris does not get inside your mouse in the future.