I was lucky enough to have some fantastic teachers to work with during my student teaching practicum. One in particular had a great rule that he introduced all of his classes to at the start of the year, by showing this particular clip:
This pretty much summed up how students should behave in his class, and students got the idea.
What really impressed me, however, was not just the memorable way to deliver the message. This teacher modeled this message throughout the year, and not just in the classroom. Even in chatting with other teachers about school politics, or war stories of bizarre people who used to work there before scandals sent them off to another career, his contribution to the conversation was always positive (or as positive as was reasonably possible).
I learned some other good tips from him, things like trying to always deal with misbehaving students outside the classroom door (where the student can be an individual and not a ringleader, and you can be a person instead of crowd control). But I think the biggest lesson I saw was the unspoken one, of living out and modeling who you want your students to be, even when they aren’t around to see it. Or, take it in the reverse – don’t demand that your students be someone better than you. (I don’t know, I’m trying to find a way to word this without falling back on quoting Ghandi.)