To illuminate a scene properly, the face of the person conferencing should always be the lightest color tone on screen. If possible, remove any white from the scene. In most cases this will include changing the color of your walls to a darker shade. Shades of blue work the best. Participants should also be reminded to dress appropriately.
Solid colors are better than complex patterns, and dark or neutral colors are best.
Stripes or busy patterns will cause the camera's focus to oscillate and destroy picture clarity. Once the lighter color tones in the room are removed, don't be afraid to adjust the brightness and contrast controls. Remember that the factory defaults assume the worst of conditions. Without the danger of white creating flare in your shot, try opening up the iris stop or increasing the brightness of the camera. When placing a table, remember to take into consideration that lighting is adjusted in relation to the participant's position at the table.