I would suggest to be confident (or at least project an air of confidence). Have met a couple of unsuccessful candidates who had decent resumes, and what (un)impressed me about them was how timid they seemed. Obviously you don't want to take this to an extreme and strut around, but be confident about your abilities and have good answers to questions like, "What do you want to do with your career" and "what makes you a good candidate?" There is nothing worse than someone who shrugs and says "i don't know" with a low voice to every question and who stares at the floor. Well, there is one thing worse, that's the guy who thinks the world owes him a favor for him allowing it to coexist with the incredible light that is his essence.
You don't want to pretend to be someone you are not. That is, if you have no consideration of an academic career, don't pretend that you do.
You also want to know about the field you are getting into. Everyone will ask you why you want to do this particular specialty, and you need to have good answers for this that do not involve something vague.
Smile, be inquisitive and enthusiastic, even if you have to fake it a little.