Lots of desk jobs require use of the mouse but it's pretty easy to forget that this can put a strain on your muscles and joints. Here are some tips on good mouse and keyboard use:

• If you have to reach too far for your mouse, it will put strain on your muscles. Try bringing it closer so that your elbows can be relaxed at your sides. 
• Make sure the mouse fits your hand. If it's too small, squeezing it can be a strain on your hand muscles.
• If your work requires you to draw, a graphics tablet can be a great option as they utilize a more natural and relaxed position for the hand and wrist.
• Try moving the mouse from your arm as much as possible. For smaller movements, use your wrist instead of your fingers.
• Take microbreaks ever hour. 15-20 seconds to shake out your arms, stretch your neck and wrists, and look away from the monitor. 

This handout from the ACA has additional details.