This article is from the Ergonomics and Typing Injury FAQ, by Dan Wallach email@example.com with numerous contributions by others.
A. Many make the common mistake of putting the monitor, the keyboard, or
both off to one side on a desk. If you perform more than a few minutes of
keyboarding a day, the keyboard and monitor should be placed directly in
front of your normal sitting position. The screen should be 18-30 inches
from your eyes or about an arm's length.