The best way to heat tortillas is one by one on a comal. This isn't always practical with a crowd so an alternative is to wrap a barely damp tea towel around a stack of tortillas and microwave for a minute or so.
You can then put the hot towel in a clay, Styrofoam (boo!) or metal tortilla holder and serve. My friend Christopher Ann will be quick to tell you that you never take the top tortilla. I'm sure she has a reason.