I was talking to a friend about teaching the other day and I got a good tip from her. She ONLY frames her rules in the positive. It made me go back and look at mine and see that I was actually doing a pretty decent job of this without even realizing. She does this because her theory is that when you tell someone they can't do something, then they want to. This is exactly the way I am, so I understood immediately what she meant.
Some tips from me:
1. How about turning, "Don't be late" into "Be on time."
2. "Don't talk when others are talking" into "Listen!"
3. "Don't speak Korean" into "Please speak English."
4. "Don't forget your book" into "Bring your book everyday."