A good dictionary and thesaurus are really useful. But you also want to surround yourself with reference books that reward idle noodling. Here are two of my favorites.

Brewer's Dictionary of Phrase and Fable. You can pick up old editions dirt cheap on the usual sites. Here's the wikipedia entry. https://en.wikipedia.org/wiki/Brewer%27s_Dictionary_of_Phras...

A Dictionary of metaphor. https://www.amazon.co.uk/Metaphors-Dictionary-Comparative-in...