Like every element of personal style, there are no hard-and-fast guidelines on moustaches (which, for unknown reasons, I habitually spell with an "o"). Generally speaking, however, I would say:

• Beards require them,
  
• Dark hair coloration is preferred (sorry, Chuck Norris, it's true), although going gray/white is not a problem,
  
• High density is better than low density, and
  
• Cleanshaven or entirely untrimmed are often safe choices.

(I'm actually aiming for the last right now.)