Remaining angry at someone was like letting them live "rent free" in your head.
The next time you find yourself in a situation that can set you off, acknowledge it and then let it go. Either find something good in the situation or just replace the thought with a thought of something you do want.
Simply go, in your mind, to some place, real or imagined, that feels good and remain there for about 30 seconds basking in the good feelings. That is usually sufficient to change your emotional state to one that is more productive. Remember the wise suggestion from the Abraham Hicks work; the most important thing is that you feel good.
It's really that simple. If you are feeling good, everything is flowing and you are attracting your desires. Anything less, and you are shortchanging yourself.
Remember, "As you sow, so shall you reap." Bible, Galatians VI