Because consumer-grade digital cameras have weak flash units, it is important to use external lighting. Otherwise, room corners will be dark, and colors will not be vibrant. And finding exactly the right way to view the room is very important. A wide-angle lens avoids the looking-through-a-keyhole appearance. I use multiple slave flash units and a true wide-angle lens (rather than a cheap screw-on adapter). Also, it's amazing how using a camera tripod improves a photo!
Typical MLS photo.	Notice that the view is much wider, all areas of the room are equally lighted, and the 'dark and dingy' look is gone.
Typical MLS photo.	In addition to enhancing the lighting, it is important to declutter surfaces and remove distracting background objects, as this photo demonstrates.