Don't forget your body language like making eye contact, your posture, not fidgeting and not mumbling.
Try not to oversell who you are.
Eat properly before - don't have stinky ingredients!
Think of honest questions to demonstrate you're curious and have researched.
Get there in time, to feel calm and ready for a great meeting.
Interact, perhaps, with the firm's twitter profile.
Do not be worried to say you don't know a response to questions.
Advice for Job-hunters:
"Before you have the interview find the info about the company. Get to know what the firm does, who their competitors are, and their principles. An interviewer won't take notice of your input if you havent researched how they operate."