It is important to use your mouse ergonomically.It is believed by many researchers that by keeping your wrist and hand in line with your forearm in a straight and neutral position, you reduce stress and strain on tendons and muscles.
Use your index and middle fingers for clicking the right and left mouse buttons, respectively.Make sure, when handling the mouse, to keep your hand in a straight line with your forearm, and not surrender to any urge to bend the palm at the writs; either to the left or right, or up or down.
If your wrists form an unhealthy angle when using the mouse, it can easily cause many aches and pains, as well as joint and/or tendon infections.