Failing to prepare is preparing to fail. Before you interview, ensure that you can speak concisely to three things—your strengths, your passions, and why the industry/company/position you're interviewing for is a great fit.
Start off right: make an impression. You've all heard the statistics about first impressions. They happen quickly and are hard to change. Be early, well dressed, and have something to write with and on.
Be an expert storyteller. Good companies know that a candidate’s past performance and behavior is the only reliable predictor of their future performance. Rehearse three to five stories that speak to your strengths, passions, and the results you've achieved.
Manage your body language. Nonverbal communication often gets more attention than what you're actually saying. Sit with an open posture (don't cross your legs or arms), sit up, maintain eye contact, and smile.
Follow-Up. Send everyone you met a hand-written thank you note within 48 hours of your interview. Cite something specific and memorable your interviewer mentioned and reiterate your interest.