TBH I agree with sniffer, get a suit (but don't go over the top). Essentially it's a job interview, so a suit is appropriate -smart, basic, plain colours (black and white / pastels works well). Avoid anything you'd wear out for drinks with your friends, sequins, glitter, or tops with pictures of cats etc on them.
Also, if you have long hair tie it back or get it put 'up' for you (if you get in, you'll be wearing your hair in a bun for hte rest of your career, and this is good for subliminal messaging - helps you to look the part) plus it stops you from messing with it while you're being interviewed.