Correction #1
Keep your hands inside your shoulders
A centered position for your hands is essential to prevent RSI. Overstretching the arm to reach for the mouse beyond the keyboard is a common trap.
By using an ergonomic mouse like Mousetrapper you get an ergonomically healthy position that keeps your arms and hands relaxed. It has been found that a centered mouse, often after only a couple of weeks, provides a noticeable improvement.