Ok I'm not a pro at this, but I've now had 4 face-to-face and 2 telephone interviews (3 of which for the same position). I think I can give ya'll a few helpful tips to get you through the scary process.
First off, dress the part. I have 1 traditional interview suit. I bought it on a whim (and on sale) a few years back at Ann Taylor Loft. It's a classic shape, classic color (black pinstripe), the skirt hits right at the knee. Yes, the blazer needs some tailoring due to weight loss and because I am in between petite and misses so I used some hem tape to temporarily fix the sleeves. Try on your suit/outfit at least the day before to confirm fit and style it with shoes and accessories. I am a firm believer that for the first interview you should dress conservatively even if you know the company is very casual. You can downplay your dress for your second and third interviews.
Second, leave your purse and cell phone in the car. I'm lucky enough to only need a key fob for my car, so I only take that a simple leather portfolio inside with me. Always bring your photo ID, your car key (1 key only) and your resume.
Third, if you're like me searching for an admin position, bring fresh writing samples. And remember your girl scout training - be prepared and bring extras. I watched the faces of my group from my last interview light up because I came prepared with samples.
Fourth, if you are moving along to the second round...think about questions from the first interview that you want to expound and write out your answers. An interview is your time to sell a product, you. So coming to the first, second and/or third round prepared proves that you are organized and can prep.
The best tip I can give you is to be yourself. Take a deep breath, let it out and relax. Remember the folks your are meeting with were once in your shoes.
So these are just a few tips. I will keep you posted as I progress along.