Learn about how makeup works!
The panelists had a great story about someone who painted their entire body silver for a costume, but forgot to properly "seal" the makeup, and left a full-body print on someone's couch. Final Seal is particularly good if you have body makeup on. Air-brushing can be good, but is alcohol-based and will leave you smelling like a gas tank. On the other hand, cream makeup can smear and rub off easily. Learn the tricks of the trade.
"I'm wearing costume dirt," explained Indiana. I don't know the difference between that and running around outside, but it's clean!"