A spray bottle filled with water is your best friend for reheating food in the microwave. Spray the top of pizza, enchiladas, whatever, before heating. Food reheats faster and more evenly, and (gasp) it's not as dry.
Wrap bread in a paper towel before heating (or thawing, if it's frozen). If it's dry, spray the towel with water. Bread is one of the few things that reacts soggily to the spray bottle trick.