For one thing, I know that your desk needs to be placed where you have full view of who comes in your office door, but not directly in front of it. Also, avoid having the sharp edges of the door (when it is open) pointing at you--this may cause some health problems.
Another office room tip I got from a friend is to avoid placing your files behind your desk--your work will never be finished! Have a cabinet for files beside your desk or placed some where else in the room.
Hope these tips help.