Dress up, a firm handshake, be confident, do just a little research about the company...

if you do not know the answer of any of their questions, just tell them you do not have that idea and you will look into it. 
if you have any recurring actions when you get nervous, work on those.

carry your resume, a nice pen, a piece of paper in a nice folder.

ohh and think of few qualities that you would associate yourself with.

Good Luck!