Wear a suit and tie. Have paper and a nice pen/mechanical pencil - TAKE NOTES. Write down everyone's names immediately and their positions (if you forget someone's name or what they do, you'll look like an idiot). Get business cards for follow-ups and thank you notes. Have a cheat sheet made up for answers to the most common interview questions. Prepare several top-notch examples of your finest achievements that you will highlight. Know as much as you can about the company. Firm handshakes. Look em in the eye. Smile; be personable. Be enthuiastic, excited and sound like you REALLY want the job. Make yourself sound like a super-star (that's what they're looking for!). When they say, "We need someone that can do/be this...," use a relevant, powerful example to show them you're their man!
Have many questions prepared for each person. Exampes: What are your 1-yr./3-yr. initiatives?; What initiative are they most passionate about?; What is the #1 quality they are looking for in a candidate? *then tell them how you posess it!*; What do they like most/least about working at the company?; What may your career progression look like?; What about you as a candidate interests them?
BE CONFIDENT and best wishes!