As previously written, there are times when we feel angry and this does not mean that we are bad. Often we have been told that anger is a negative emotion and so we feel that we have failed because we are angry.
There are times though when anger is destructive and so we should not allow it to get the better of us. When we allow anger to persist, it grieves the Holy Spirit. (Eph 4:29-32)
The basic cause of anger can be selfishness - some one has interfered with our rights! We will not always have our way though and we need to come to terms with this.
Firstly, we have to believe that God has our best interests at heart. A person may have wronged us but a person is just another human being.
Rather than holding onto our wants and desires, realize that there is a greater vision beyond that of our own. Often our idea of fact is merely our personal perception or opinion. That means that we could be wrong. Therefore we cannot be precious about our version of facts and truth.
Surrendering our quest of rightness enables us to calm down and some times see God's bigger picture. Praying that God's will be done rather than selfishly pressing on to get our way, is also empowering.
We should learn to back down, take a breath and incline our mind and heart toward God.