- Wear makeup. It makes you look less shiny in the lights and keeps the stage from washing you out. Male or female, a little foundation and blush never hurt anyone. Just match your coloring and blend thoroughly.
- Do your hair. Hair is actually part of your costume, believe it or not.
- Wear a costume that goes with your body type. You expect certain physiques for certain races, and mixing and matching doesn't work as well as you might think.
- Consider your stage presence. While not crucial, there's "drifting gracefully" and then there's the guy who walked across like it was his mom's kitchen.
- Watch where you hold your props. One contestant covered her costume with her shield by holding it between her and the audience the entire time.
- Spit out your gum. No elaboration needed.
Some of the costume people were attractive, some weren't, but at the end of the contest, you admired the people who made costumes that went with their look as a person and didn't try to be super-sexy if they weren't -- thinking in particular of the two older women who went orc and dwarf (they ruled) and a plus-sized person who filled out a moonkin outfit admirably.
I also admired the ones with really great tailoring. Some of the sexy female costumes didn't look sexy because the tailoring was off (one attractive woman looked very saggy because her chestpiece sagged), whereas the tailored ones made you go "That's great."