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I love middle schoolers. In fact, they're our biggest group.

I also interview loads of potential instructors for online positions, but before that, for our intensive 3-week summer residential programs.

All the above advice listen to. In addition:

1. Always write a thank you note to everyone concerned when the interview is over.
2. Always do your homework. Learn everything humanly possible about the school/district. This is the #2 reason we don't hire people. If they can't be bothered to know what "CTY" stands for or how we identify gifted kids, we can't be bothered to teach them. Analogous situation with any other institution.
3. While Colin is right that you never answer a question with a question, come prepared with questions to ask. And, if you aren't invited to ask questions, you probably don't want to work there.
4. Look for a strong support system. Not a toss-the-newb-into-the-pool approach, but some kind of organized mentoring and monitoring system for newbs.
5. If you get to take a tour during classtime, ask to take a stroll past the classrooms of the newest hires. You don't need to go in. Just need to look through the window to get the feel of how the newb is doing.