...Or at least I didn't know it until I read this post. It's something that I was doing before at least semi-intuitively, but consciously paying attention to this tiny fix is such an easy way to instantly give a room a more polished feel.
Basically, forget about centering art on a wall, and pay more attention to orienting it around the furniture. (This doesn't necessarily mean always placing it dead center above a major piece of furniture - although it could - but rather just thinking about the art as it relates to the way you've arranged the pieces in your room.)