Be flexible. Eleventy million things can (and will) go wrong. The PE teacher will be out sick. Someone will throw up. The interventionist will need to change group times just this once. You will have three different parents show up with 30 cupcakes each on the same afternoon without checking to see if it was ok (true story). Just take a deep breath and a swig of your caffeinated beverage of choice and go with it... It will all work out in the end!
Become BFF with the janitors. Make your kids pick up trash, wipe the tables, etc...anything to make the janitor's life a little easier. They notice these things! They tell me all the time that I have one of the cleanest rooms in the school. And anytime I need something, they don't hesitate to help me out. (This may just be because we have the sweetest janitorial staff EVER. But still...be good to them and they will be good to you!)
Have fun! I'll never forget...towards the end of my first year, one of my students was dead serious when he looked at me and asked, "Do you even have a job?" It cracked me up and I took it as a compliment. He didn't see all the work I put into every single minute of our days together. He just saw his teacher having fun and making memories. So find a way to make learning fun. And take a few minutes to sing a song, do a craft, tell them a joke, let them teach you how to Dougie... They're kids; fun is their language!
My biggest advice to anyone, in any situation, at any point in time is this: laugh it off, learn from it, and let it go! I tell people all the time that I laugh at myself first and foremost...and most often! You have to find a way to laugh at yourself. Don't ever take yourself too seriously. (Now, our jobs are definitely serious business, but there's a difference in taking pride in your awesome work and taking yourself too seriously.) We all make mistakes every single day and the beauty in that is the opportunity to learn from them and grow. I don't mind to make a mistake or two (or thirty!) in front of the kids--they need to know that grown ups make mistakes and they need to see how responsible adults handle their slip-ups. And after my mistakes have been made and I've laughed at myself and let others laugh along, I let it go! Don't beat yourself up over every.single.little.thing. Let it go, because it happens to everyone.
...and that's all she wrote. I can't wait to read all of your awesome advice!