To promote comfortable leg postures, consider the following:
Clear away items from beneath your desk to allow comfortable leg positions and movement.
Use a footrest if your feet do not rest comfortably on the floor.
To minimize reaching and to promote comfortable shoulder and arm postures, consider the following:
Place your keyboard and mouse or trackball at the same height; these should be at about elbow level. Your upper arms should fall relaxed at your sides.
When typing, center your keyboard in front of you with your mouse or trackball located close to it.
Place frequently used items comfortably within arm's reach.
Get up often even for short breaks.