There are many reasons to get angry, but all of them lead back to ego.
Ego is the false self that is a created cog of this world. Ego is the heart of vulnerability and selfishness. Ego is separateness from God and others.
With any negative emotion (anger, sadness, rage, resentment, boredom, apathy and others), the best thing to do is to be aware of the feeling and the one creating that feeling (yourself). Take 100% responsibility for not only creating the feeling, but also for everything in your environment which "apparently" triggered it. When you take 100% responsibility, you can no longer be a victim.
Realize that nothing is important! Nothing! Only with this can you give unconditional love.
If you find any of this difficult, then step back from your body several million miles. Look at that tiny dot of light, called Earth, and realize how small your problem is compared to the rest of the universe.