In all of the classrooms I do a lesson on anger management. I focus on having the students come to realize what their anger "buttons" or triggers are, how their body feels when they are angry and various relaxation strategies to utilize. Often I read children's literature to help the students relate to the characters and to show them that being angry is a very natural emotion. I stress that they can learn how to control their anger so that it doesn't boil over and lead to making poor choices. It's important for students to realize what makes them angry so that they are aware of these triggers and then they are better able to calm themselves down.
In the classrooms we practice many various deep breathing exercises, movement activities that lead to relaxation, thinking happy thoughts/places that are calming, and counting backwards. The students also brainstorm what works for them to calm down - exercising, reading, being alone, having a snack, singing/listening to music, writing or drawing. It helps the students to hear what helps others because then they can possibly incorporate those ideas into their own lives.
If you are looking for some good children's books that address anger I would recommend; When I Feel Angry by Cornelia Spelman, Howard B. Wigglebottom learns to back away by Howard Binkow, Danny the Angry Lion by Dorothea Lachner, and When Sophie gets Angry, Really, Really Angry by Molly Bang.