Plan interview travel arrangements so that you arrive with plenty of time. Take out any possibility you could arrive late.
Pick out your interview clothes at least four days ahead of time. This allows time to get the suit dry cleaned and pressed.
Wear a color besides black. 95% of interviewees will be wearing black. A great way to stand out to the admissions committee is to wear some color like gray, green, or blue.
Prepare some questions for the admissions committee ahead of time. Thoughtful questions from an applicant show that you are serious in finding a school that is a right fit for you. After all, four years of schooling is a big commitment.
Practice answering common questions asked in dental school interviews like "Why Dentistry?" or "What is you greatest weakness?" When you answer, practice smiling, sitting still, and not saying "um."
The night before, read over your application. Anything in it is fair game for you interviewer to ask you about.
Get a good night's sleep.
On interview day, be friendly with the other applicants and relax. A well prepared interviewee is a happy interviewee.