I've been in a lot of interviews so let me tell you what I know
1. don't lie, just don't. Say it how it is, if it needs to explained, then do so after stating the fact, not before.
2. don't allow for quite moments, if they aren't saying something and you have nothing to say give them a mirror... as ask them about how they got to their position, do they enjoy it, etc.
3. research what your position would entail, have questions to ask about it.
4. connect on a personal, if they tell you something about themselves and you think it relates to you or share a similar experience, share it, but make it short and quick.
5. Thank them for the opportunity and tell them how you feel about what you heard.
6. Dress for the job.
7. be 15 minutes early, not an HOUR, if you arrive an hour early, don't announce yourself until 10 to 15 minutes of your appointment.
8. Relax and don't take the rejection personally if comes down to it, bitterness won't do you any good.
I've gotten rejected from jobs who referenced me to other jobs because they liked me but for whatever reason I wasn't the best candidate.
9. STRONG body language, open chest, no arms crossed, no slouching, no hands in pockets, no direct eye contact, but don't look down, here is a tip about eye contact.
When they are talking always look at them, when you are talking, look at them when you start to respond, then break eye contact and start using your hands as you talk to express yourself. And make new contact at every new point you make in your response or every other sentence. OR when you finish a thought. (pick whatever is easier for you)
I know people say strong eye contact is good, but that's a myth, looking at the interviewer head on through out the interview is just creepy.
Lastly if you have glasses where them, a study shows that employers view people with glasses more reliable for some weird reason don't ask me why.