I have found that if you have difficulty getting some students to join the class, I have them write things on the white board that I usually write or draw. It changes their behavior and they feel important and part of the class.

We have a standard set of S.O.P.'s for the school and discuss expectations of the students of the particular class. These are shown on a powerpoint overhead. Any questions from the students are welcome. Trick is, get the students to remember them.