Wear your hair down, preferably in a fluffy layered cut, and be sure it's frosted, streaked, or dyed a completely unatural color. Avoid red dye, though, as it actually was popular in period. Nail polish should be bright. Lip gloss, foundation, blush, and mascara should all be worn. Eyeshadow should be electric blue.
Dreadlocks are nice, too.
For both sexes, tattoos and peircings should be abundant. Take Care of Your Costume While this wouldn't seem desirable, it can lead to stunning tours de force of Bad Costume. These notes were compiled by Margo Anderson, who has, regrettably, seen every one of the above examples at the Renaissance Pleasure Faire. This page has been on the Web for less than a month, and has been copied repeatedly. I'm glad that you like it, people, but please don't do that.