"Check in" and confirm the interview time and pronunciation of the interviewer's name if necessary.
Take your lead from the interviewer as far as introductions are concerned: use clear speech and a firm handshake. Do not smoke or chew gum even if invited to do so.
Show enthusiasm for the interview and job (even if it's not your first choice!) by maintaining sufficient eye contact, varying your tone of voice appropriately, being clear and concise in your answers and questions, and by maintaining good posture.
In answering questions, give a general answer ("I believe my analytical ability is my greatest strength"); be more specific ("That is, I try to keep people informed of what's going on"); and finally, give an example or two ("When I was President of my fraternity I established our first newsletter and held weekly meetings with each committee chair").
Be ready for unusual questions or approaches and don't let them throw you. If an interviewer says, "Okay, begin...," be ready to tell about your interest in the job and organization, to highlight your abilities and relevant experiences, and to ask appropriate questions. If you're given a hypothetical situation/problem and asked how you would handle it, take a moment to think about similar situations you've heard about or been in and then answer as best as you can.
At the close of the interview, bring up any of your positive points that you may not have been able to cover earlier and ask the interviewer for feedback, both in terms of your suitability for the position and how you handled the interview. (Then use this information to improve.) If really interested, ask for the job.