Just some thoughts as I'm rolling through interviews:
1. Don't wear jeans and wrinkled t-shirt on the day of your interview. (Not me, someone else interviewing in the lab next door).
2. If you are presenting from your laptop, please bring VGA and DVI adaptors (Like I do). Invariably they don't have the one you need.
3. If you are presenting from your laptop, clean up your laptop (Don't leave talks from prior interviews on the desktop or anything compromising for that matter).
4. If someone asks you where you are interviewing, just be frank and tell them. If you don't you just come off as a slippery eel.
5. Clear some space on your credit cards if you are doing multiple interviews back to back. Some places make you buy your own plane tickets, hotel rooms, transportation, etc and then reimburse you (this is dependent upon the institution and its purchasing regulations). This begins to add up really fast.
6. I always ask everyone in the lab what's one thing they wish they could change about the lab. This question usually is a kind way of asking them what they think is something negative about the lab and leads them to answer candidly. I also pose the same question to the PI but I rather ask it as what are your current and future challenges you face with the lab. This usually elicits a pretty good response and you get an insight into what PI is battling with in the lab and finds important.