Wow. Good luck to you.
I was a classroom teacher for 7 years, and have done some substitute teaching since resigning my classroom position. I never had any problems as a sub, because I already knew what to do in a classroom, I know what to expect, I know the "tricks", I know what to say and do when certain situations arise... not to imply that you don't know what you're doing, but having 7 years of classroom experience helped.
Thats being said, just the fact that a sub is there changes the dynamic of the classroom. The kids aren't the same as they would be with the regular teacher, and no amount of experience will change that fact.
The biggest challenge I think subs have is classroom management. There's lots of things you can do to make sure that the class runs as smoothly as possible:
1. Call the students by name; if the home teacher didn't leave a seating chart, make one.
2. Get the kids working/engaged right away. Do the "business stuff" (attendance, handing out/collecting papers, etc) once they've started.
3. Follow the classroom teacher's rules *as he or she left them*... if the rules say no gum chewing, don't let them chew gum, even when they kids say "but she usually lets us!"
4. Don't engage the kids with arguing about what is and isn't allowed. I call any kind of retort detailing why they "should" be allowed to do or not do something "arguing". Example:
--but I was just...
--I need to...
--he said I...
Further, have a line ready so when they "argue", you put it to rest right away. Something like "This may not be what you're used to, but this is how it's going to work today. Thank you."
As a classroom teacher, I said "I don't care" a lot... as in "I don't care why you're up, please sit down". You might not be comfortable with this technique
5. Being the students' "buddy" never works... it just invites them to push boundries.
6. Please and thank you work wonders! These little words will show that you respect the students AND eliminate the posibility for discussion.
7. Get to know the teacher next door; he or she can be helpful.
8. Get there early and be prepared... have the papers in order, have stuff on the board already, materials/manipulatives ready to be passed out, etc.
9. Don't be afraid to call home! "Hi, this is Ms. AuburnChick
and I'm subbing for Mr. Science Teacher today... Joey was in my class 4th period, and I wanted to let you know what happened today..."
10. Leave detailed notes for the regular teacher, both good and bad stuff!
11. Don't leave directives up for discussion... There's a difference between "Susan, will you please sit down?" and "Susan, please sit down".
12. Sending kids to the office is a last resort. Tell them to move their seat, stand in the hallway, whatever, and then talk to them, privately (instead of berating them in front of their peers).
The best thing you can do is go in there and know what you're doing. Even if you're not sure, pretend; if you look like you don'tknow what you're doing, the kids will pick up on it and all hell could break loose!
Finally, only offer to sub in classes where you *honestly* think you'll do a good job. As the music teacher, I got subs all the time who just thought it would be fun to sub for music, and then they had a hell of a time in the classroom
Again, good luck!