Your hair should be neat, clean, and conservatively styled. Banana clips, brightly-colored scrunchies or elastics, and cheerleader-type ponytails look out of place with a suit. You may want to wear your hair in an updo, pull it back into a low ponytail, or wear a barrette (this suggestion does not include the tiny little barrettes that only hold the front of your bangs back). The idea is to look polished and professional, not to advertise what a creative genius your hairdresser is.