I picked a few "What not to Wears" based on outfits I've actually seen during recruitment. I didn't come up with one for pref, because the only one I could think of was the prom dress, and that was well covered earlier.
Open House:

As many people have said, it's important to impress girls, not guys. It's also important to dress for the occasion. A corset or a micro mini skirt, and certainly the combination isn't appropriate for recruitment. That's club/show wear. Even on campuses where knee-length is a little dowdy, you need to keep your butt cheeks covered. Sit down in the outfit to make sure you can do so without flashing.
Casual Night:

Where is this outfit appropriate? The pool, the beach, hanging out with friends in the summer time. It's not ok for recruitment. Avoid the super-distressed look on your denim, and the itty bitty shorty shorts. Also, if a tank top/tee is appropriate for your campus's recruitment don't pick one with a slogan. Why? Because then your clothing is talking for you. You don't get the chance to send a message about who you are when your shirt does it for you. "Don't hate" is asking for someone to hate, so a recruitment party isn't the best place for it. (Other offenders have included "I'm hot" and "Your boyfriend wants me".)
Theme:

Two problems. The first is that a dress that is shrinkwrapped isn't appropriate for recruitment (or work, school...). Nor is a super super short dress. The second is that you don't want to be ALL one color. You'll be remembered as "the blueberry girl" or the "pink girl" or the "green girl" instead of "the really funny girl that ran track in high school and likes to sing"...you get the point. Everything doesn't have to match, it has to
go. If you want to keep it simple, go with something like a black dress and black shoes with an accessory in a color, or pearls.
ETA: An outfit can be cute and not be appropriate
for certain places/occasions. The casual night combo is an example. Fine at the beach, mall, pool. Not at work, recruitment, job interviews. And though it is very important to look well groomed and appropriate, it's also important that you worry far more about meeting actives than about your clothing. If you're self conscious, you won't be able to enjoy yourself and it will show. Be comfortable, yourself, and appropriate and then
be confident.