1. Be wary of giving the kids control. The term "give them an inch and they'll take a mile" is so very very true. If I let the kids if I let one of the kids read one page and I'd read the next it quickly degraded me reading to them.
2. Beware distractions. Anything and I mean anything can serve as a distraction. One of my kids would look out the window. He'd point at a cloud and say "that's weird" in order to distract me from the work at hand. He would point at anything in order to do this. Houses, wall hangings, his shoes I mean anything.
3. No one ever has to go to the bathroom during recess, but once you get things settled down arid start trying to get the kids to get on task suddenly everyone's bladder is full to the brim.
4. Don't try to make friends with the kids at first. They will walk all over you. Once I realized I was supposed to be more of an authority figure and less of a cohort things worked much better. Don't be afraid about being stern.
5. Make sure you know the rules. At Eastside Alternative School, where I volunteered, the kids have a lot of freedom. We had a sub who didn't know what was going on because she had spent most of her time with more strict schools. Children referring to adults by their first names shocked her. Students going into the hall to work quietly without asking seemed immoral to her. Her lack of knowledge confused the kids who weren't doing anything wrong by Eastside standards.
6. When in doubt ask. You're not expected to know the ropes but if you don't ask you won't find out. I blundered around for my first few weeks, the adjustment would have been much easier if I had spent 15 minutes with my advisor and admitted my ignorance.
7. If you want to work with a great bunch of kids and really nice teachers go to Eastside. It was a great experience and quite eye opening. When they say alternative school they aren't kidding. The difference for my grammar school is astounding.