As a class, we discuss our common expectations of behavior in the classroom and come up with a set of classroom procedures which are posted in the classroom. Additionally, I do have one guideline that I believe is the most important.

I like to state my rules, procedures, and guidelines as positive statements (such as “be courteous”), so the main rule in my classroom is:
Always allow learning.

However, I know that this comes across more clearly when stated in the negative as:
Never hinder learning. (including your own learning)