Simply telling yourself, "I should not be angry right now," will usually not calm you. Moreover, if you lose your temper and tell yourself you shouldn't be angry, you are apt to feel excessive anxiety and guilt in addition to the anger.
Rather, try to be aware of what specifically is making you angry. (For example, "It's awful that he is talking to me this way.") Once you give up those anger-causing self-statements, you will feel less anger.
Challenge your self-statements that lead to anger. ("Why is it so awful if he talks to me this way? I might not enjoy it, but I will not take it to heart.")
Once you perceive someone's behavior or words in a positive or even neutral light, you will not be angry. ("He's speaking to me that way because he cares about me and wants me to improve." Or, "He's talking this way because he is personally upset.")
(Rabbi Pliskin's Gateway to Happiness, p.199)