Gary Rubinstein doesn't buy the adage that rules--for students or for teachers--must be stated positively, without don'ts or nots. So he lists 10 rules for things teachers must not do in their first years. Tops on his list is "Don't try to teach too much in one day," which Rubinstein says is a common mis-step because teacher preparation programs, especially fast-track ones, overemphasize having high expectations for students. Among Rubinstein's list of don'ts are: don't teach a lesson without a student activity; don't send kids to the office; don't allow students to shout out answers; don't make tests too hard; don't be indecisive; don't tell a student you're calling home; don't try to be a buddy; don't dress casually; and--last but not least--don't babble.