Step in and stop it immediately: ​When you realize your child is about to become violent or aggressive, remove him/her from the situation. You don't want to give the child too much attention, just enough to tell them that their behavior is not acceptable.
Lower your voice, don't raise it: Children always take cues from their parents. If you raise your voice and yell at them when you're angry, they are going to do the same thing when they get angry.
Practice ways to de-fusse your childs anger: You need to help your child realize that anger is an important emotion, and it can be controlled. Have them express their emotions in words, or even have them count to ten or take deep breaths. These methods can help take the child's immediate attention off of their anger, and onto something else.
Teach kids that aggression is wrong: You should try to teach children that aggression is wrong when they are calm. You need to slowly explain that aggressive behaviors will not be tolerated.
Tell your child to "Use your words": Many children who are aggressive are simply just lacking the communication skills to help them through stressful situations. Teaching them simple words like "No" and "Stop", can help the child get their point accross without having to resort to violent behaviors.
Recognize your childs limitations: You need to know in what situations your child becomes aggressive in. If he/she becomes aggressive while playing certain games, or with certain people, try to keep your child from playing those games or being around those people.