Describe the specific misbehavior or disruption you would like assistance with. Don't talk too much. Give them opportunities to work alone, with a partner, or in small groups of between 3 and 5. Break the class period into two or three different activites, but do try to make each activity segue smoothly into the next one. Begin at the very start of the class period and end at the very end of the class period.
Some teachers have something on the board for the students to do as soon as they enter the room.
Don't call roll. Use your seating chart to take roll while they are doing something. Keep all of the students as actively involved as possible. Don't do things like take turns reading aloud, which only occupies one student at a time. When one group does a presentation of any kind, the rest of the students should be involved in evaluating that group, preferably with a rubric.