Over the last couple years, I've been exploring this. I can't provide any answers, but I've found all the usual recommendations useful. CBT, Watts, Stoicism, yoga, mindfulness.

Of those, the last -- mindfulness -- has been the most crucial.

I cannot usually control my reaction to stimulus, but the hardest part for me (and in others, now that I observe them) is the identification of the event trigger.

Once you identify what causes things to happen[0], it's much much much easier to adjust the behavior. The event notifier pattern has been most useful for me.

[0] after all, it's kind of ridiculous that a bad incident in traffic will affect my interaction with a colleague.