Wear the most comfortable shoes you can find, such as running shoes. Walk up to your standing desk and adjust the computer monitor so it is at eye level. Place a phone book or other sturdy support underneath the monitor if you need to raise it higher, or adjust the desk's monitor shelf if it has one. If you use a laptop at the desk, set the laptop so the screen is near eye level. Angle it back some if necessary for optimal viewing.
Shift your weight from one foot to another frequently while working to avoid leg and foot fatigue. Rest one foot on a stool or chair rung occasionally, or lean slightly against your desk from time to time. Alter your position once in a while to decrease potential foot tiredness or discomfort.
Place an anti-fatigue mat in your standing area after a day or so if your floor is not carpeted or if you need the extra support and fatigue relief a mat offers.
Take occasional sitting breaks to give your feet a rest. Use a tall stool or tall chair so it's still comfortable to sit near your desk when necessary. Walk or pace around the room for additional breaks from simply standing in one place.