Similarly I find it useful when some little thing is irritating me. I can't remember where I read it, I think it was related to Marcus Aurelius, but basically the idea that when something negative comes up, either say/do something, or let it go.

That person who just cut in line in front of you? Say something, or let it go. That guy on the plane obnoxiously tilting his seat way too far back? Say something or let it go.

As soon as I think that to myself, I let go and feel a wave of indifference and serenity.

These are of course pretty minor examples, but also really common everyday occurrences. Like, practice.