1) When you're really stressed out- stop teaching....
Instead, play games, do puzzles, or read with the students... Be SILLY and have FUN with the students to remind yourself why you went into the profession! It might sound simple, but taking a 15-30 minute break from teaching to really play with the students will almost always put a smile back on your face!
I realize you can't keep every letter, card or gift from students, friends and family... but make sure you keep a few for when you're feeling down! I have a little box and a folder in my classroom full of things from previous students, my husband, friends, etc. that always make me smile. If I'm feeling super frustrated or overwhelmed, it's so nice to be able to just open the folder and look at a few things inside.
3) Never take your computer charger home!
I think it's a little unrealistic to tell you to never bring home work, but a few years ago, one of my mentors told me to always leave my computer charger in my classroom. Her rationale was amazing- if you leave your computer charger in your classroom, you can only work as long as your computer battery will last without being plugged in (probably only a couple of hours). This will let you get all the super important work done at home but will hopefully keep you from spending 8 hours on a Sunday planning.
What tips do you have for avoiding burn out?