If you've picked out the dress of your dreams, and you've decided to bring it along with you, be sure to follow this advice:
Bring your dress with you on the plane as a carry-on. Don't check the dress, pack it in a suitcase, or do anything that might cause your gown to be misplaced. A flight attendant will be happy to help you stow the dress in an overhead compartment, or sometimes, they'll even help you put it into a coat closet or area reserved for things like strollers and wheelchairs (if there's room).
If you're the groom, the same advice applies. Pack your tux or suit in your carry-on bag.