If we accept that anger is unnecessary and counter-productive, that is only the first step. Any unenlightened being can become angry so, while we are still unenlightened, there is nothing we can do to stop if from arising altogether. That is because there is still unresolved karma that we have to face. However, we can reduce the frequency with which it arises and, when it does arise, we can stop it from building on itself into a boiling rage that would cause us to make more bad karma for ourselves by taking revenge, the result the Buddha warned against. The way to achieve that is simply application of the four foundations of mindfulness (mindfulness of body, feelings, mind and mind objects) during our daily lives. Awareness of the anger and of the fact that it is unhelpful are the first and second steps to stopping it from growing stronger.
The third step is to reduce the delusion that is the cause of the anger. We do this by practicing meditation in a retreat setting so that we can gain a greater insight into the true nature of the body and the mind. Clear understanding of the four noble truths (the truth of suffering, its causes, its cessation and the path leading to its cessation) is a sure way to reduce one’s anger. We don’t get angry when we see the birds flying because we understand that birds are simply playing their part in the nature of things, a series of causes and effects. A similar understanding of the mental and physical world will not lead to anger because the anger is replaced by an acceptance of the way things are and the effective ways to have a positive influence on the world. With that understanding established, forgiveness is a forgone conclusion.