Check out benebaby's Makeup Inspiration thread over in the
tutorials section. Some great examples there!
Brainstorming is the way to go, though- what do you think of when you hear avant garde bride? Futuristic, maybe a little Goth or Punk inspired? What else? You can do face/hair that is opposite to the clothes, or something that matches. So, if the clothes were sort of precision cut and moddish, maybe hair would be teased and worn in, perhaps with bits of feathers or other ephemera added. Makeup could then go sort of dark and smudgy and imperfect. Or they could match - hair could be sleek and precise, and makeup could be very exact.
Elements - earth, fire, water, air, metal and ether (last two are from feng shui). Just pull from the colors you associate with each element.
Masquerade Ball is a fun one - consider masks of some sort - bits of chiffon or lace over the teyes, or painted on with cosmetics. High arched patent brows like Pat McGrath for Dior a few years ago. MAJOR lips. Beauty spots, even. Marie Antoinette type of thing. Or something more sinister?
Anyway, whatever you do will be super cool and very, very fun!
-b.