Go in there wearing a t-shirt that says, "Fuck This Interview".
Nah, seriousy bro. I know its important to you so here is what I suggest. You need to rehearse everything your going to say a few nights before. Practice practice practice. You need to have your shit down pat. The guy/girl giving you the interview knows they are intimdating to you. If you crack under pressure to them then they will know you will crack under pressure during the job. You have to go in there with confidence. You have to go in there knowing you will win this interview just like you will handle the current situations that the job will call for. Go in there with a great big smile, and act like you don't give a fuck (in a sense of course) but yet act like this is nothing to you. I mean you either get the job or not, so don't let your nerves get the best of you. Remember this guy is on your team as well, I mean, hell your going to be working with him or she. Don't be to straight forward, and don't oversell yourself. Yet again don't answer their questions like a robot either. Answer them with personalilty. They will relate to you much better. This will also show natural confidence. For instance, bring up things you might have noticed going to the interview. The parking, the design of the office, the people working at the moment, try to act like the environment is already home to you. Remember this is nothing. You can handle this. Try and pick up on things surrounding the interviewer's office and make coments about them. For instance if they have some type of memorabilia siting around try and do your best to relate to that AT the right time. Do not, bring up things about the family photo's sitting around. That is to common and shows your a kiss ass. In a sense, you don't want to act like your desperate for this job, but would like to handle it because your looking for something different and it interests you.
Anyhow, that is a few I can think of off the top of my head. Hope I helped out.
Peace,
VG