You should have a resumé and cover letter prepared. Send them to a potential employer, and make sure you bring copies to the interview. If applicable, consider taking a portfolio or work samples. Assignments from key classes or work published in student organizations are very appropriate. It is wise to have a faculty member review your portfolio before you present it to a potential intern employer.
Show your interest in the organization. Research the organization, understand what they are known for, who their clients are and typically how interns are utilized. Consult with classmates who may have interned there before.
Prepare a list of questions to ask the interviewer. Many times, an interviewer will ask you if you have any questions, so make sure you do. Ask about primary intern responsibilities, employer expectations, challenges and opportunities.
Arrive at least 15 minutes early. Check out the location of the internship before your interview, so you know how long it takes to get there and where to park. There is nothing more stressful and damaging than arriving late for an interview.