In many cases, applicants are selected because they look like what the employer had in mind. You cannot control an employer's preconceptions, but you can control how you look, and how you look may influence an employer's decision to hire you. For internship interviews, you should always dress professionally. Female applicants may wear a suit, a conservative dress or a skirt and jacket. Males may dress in a business suit or jacket and tie.
Good grooming is essential and includes neat hair, nails, and shoes.
Make sure to arrive 15 - 20 minutes early to mentally prepare yourself and relax. Upon introduction, shake the recruiter's hand firmly. Be aware that you are being evaluated from the minute you walk into the room. Maintain good eye contact. Pay strict attention.