Arrange your classroom in a way that prevents undesired behavior. Space desks a few feet apart to discourage students from talking to one another during independent work. Keep quiet areas, such as the reading nook, away from louder areas to prevent students from distracting one another during these activities. Designate a place where students can go to "cool off" if they feel upset or angry. This will make them less likely to act on these negative feelings once they've had a chance to calm down.
Establish clear and concise classroom rules. Encourage students to contribute to this, and hold a class meeting specifically dedicated to writing both rules and the consequences of breaking those rules. Students who take ownership of their classroom rules and understand the consequences to their behavior are more likely to follow these expectations throughout the year.
Prevent unwanted behavior through role-playing. Ask students to act out various situations that may occur in your classroom, then demonstrate ways of properly handling the situation. For example, write a script that involves one student bullying another. Ask select students to act this situation out in front of the class. Divide students into groups, and have them rewrite the skit demonstrating two different ways the students in the scenario should have handled the bullying situation. Providing students with tools and ideas on how to handle scenarios before they occur will reduce undesired behavior when the actual incident arises. For preschoolers or young elementary students, use puppets and stuffed animals to relate to them.
Reward good behavior in your classroom. Praise students when you see them displaying acceptable behavior. For example, point out a student who raises his hand before speaking; you can state say to him in front of the class, "Thank you for raising your hand before talking." Doing so keeps the focus on positive behavior, rather than on the negative ones. Students will in turn learn it is the good behavior that gains them your attention. Therefore, this will reduce undesired behavior in your classroom.