Find or buy a gray skirt and a white collared shirt. Then find a tie that has red
and gold stripes. Then wear a gray shirt over it. After that find or buy a black cape.
Then make your hair puffy then, well your Hermione Granger, one of Harry Potter's friends.
Thanks to a Harry Potter fan for this great idea!
Another Idea
I was Hermione this past year :) I was also Hermione at the HP 5 release party at Borders. My hair is naturally poofy ~giggles~ I wore my dad's grey socks ( as knee socks :P) the plaid skirt from when I had a school uniform, a white blouse, dad's red tie, and a black velvet cloak/cape kinda thing :) ( And I got a stick from the woods to use as my wand, hehehehe)
Thanks to Josie for these additional ideas!