Just as being a tween is a transitional time, so is everything a tween likes. Tweens spend a lot of time in their rooms and need to have a flexible decorating scheme. On Monday, your tween may sleep best with the bed under the window, but by Thursday, he or she may think it works better on an opposite wall.
Changing furniture around is a cheaper way to satisfy your tween's decorating whims, so make sure everything is moveable. Avoid wallpaper, murals or anything else that can't be changed. A coat of paint is a cheap and easy way to change a room's look in a snap.