I can’t tell you how many times it had saved my ass. I have two, one for translated idioms from Russian to English and back, and another one called Dictionary of American Idioms.
This kind of piggybacks off yesterday's post, on searching books when you don’t know how to say something.
Think of an image or a word, then look it up and read all the idioms connected to it. It's folk wisdom. It's language history. You can’t go wrong by picking out one or the other.
It’ll add authenticity to your writing, and especially to your dialogue.