I am at the stage where I dont expect to hear anything... but I still do jump 12 feet each time my work mobile rings!
The biggest piece of advice I can give, and one that was relayed to me that helped me a lot, is to smile, lots! Have a good time, enjoy the interview! Someone kindly told me that in their interview they made the interviewer laugh, and they felt like they had a great time!
So relax, get there in plenty of time (dont be like me and fly by the seat of your pants in regards to timing of my last interview), take a deep breath, sit upright, be aware of your bearing and poise, and smile! Take your time with the questions, and ENJOY IT!
Walk out of there knowing that if you tried your best, put in 100%, then thats the best you could have done on the day. Save the AAR (After Action Review) for another day!
Good luck!
JB