Whatever you wear, it should be a neutral, quiet, tasteful frame for the most important part of the picture of you want them remember - your content, enthusiasm for the opportunity, memorable strengths stories and winning personality.
Be time and place appropriate. When in doubt - be conservative and dress up - up to promotion you will earn, when hired, or the profession once you have graduated. Have them see you as a great representative of the institution. Show them the respect they have earned. Don't let anything that you wear, creating your overall visual first impression, detract from the substance you have worked so hard to clearly present to them. Remember, any networking event or "informational" interview counts, so be sure to "dress up" appropriately for these opportunities.
For Adults or graduate school interviews: wear a suit (dark navy/dark grey/black). For men, collared dress shirt and nice tie. For women, pantsuits work in most industries, wear a collared shirt or a suit blouse. You can always check out what people wear if you visit their parking lot at a time when there is foot traffic.
For College Interviews: If at a downtown law firm at 5:00 pm, be a bit more professional. If right after school, at a Starbucks or local coffee shop, wear something nice, but something you could have worn to school. Wear what your conservative grandparents would like, if they were taking the family out to a nice meal or during a formal Thanksgiving.
Boys: Wear a collared long sleeve dress shirt and nice pants. A tie is optional; only wear one if you feel comfortable doing do. A polo shirt and khakis also work well, but bring a sweater or jacket to finish off your look.
Girls: Wear a nice top and pants or skirt. Carry a sweater or jacket, to finish off your look.
Shoes: Dress shoes work best (unless it takes place at an outdoor or recreational environment). Make sure that you have already broken in the shoes as you might be doing a lot of walking and want to be able to walk, not hobble. Shoes should cover your toes and heels not be too high. Boots with low heels work so long as they are discrete. Be sure to make sure that whatever you wear they are polished, front and back!
Jewelry: Think tasteful, small or none at all, do not wear anything that dangles from the ears. Avoid anything that makes noise. Consider wearing a watch. If you have body piercings or body art, consider hiding the art and removing jewelry from the non-ear piercings. Females, wear one earring per ear. Males, if you wear earrings, consider removing them.
Fragrances and Cologne: Don't put them on or spray them in the air and walk through them. Many people have fragrance sensitivities. Less is more when it comes to jewelry and fragrances.
Hair: Get a haircut a few days before the interview. Make sure that they can see your eyes. Anyone can use hair product. Females have more options and can also use combs or barrettes. If anything moves our eyes are attracted to it. If you pin/pull back your hair; you won't play with it! But, use caution wearing your hair in a tight bun, if you aren't a dancer.
This advice does not apply as much if you are applying to an art, fashion, performing arts school or workplace where style or individualism is an essential part of the entrance/job requirements. Show something of yourself, in an accessory perhaps, just don't overdo it. You don't want them staring at your outfit, distracting them from what you saying.
Above all, road-test anything you wear. Can you sit down? Is anything a bit tight, wrinkled, not supposed to be there, e.g. price tag! Women, bend forward from the waist and look at yourself in a mirror, from the front and then the back. Make sure nothing inappropriate shows on top or bottom. You want to make the interviewer feel comfortable and respected. Let your message be shown in your well-considered stories and talking points, not in any possible negatives arising from the visual or olfactory first impression!