Reference materials for illustration are completely different than those used for writing, but for either task I look at everything I can get my hands on. I examine both online and library sources. When possible I go to relevant locations and exhibitions. I talk to people with first hand knowledge. The specifics vary.
A constant companion for all writing is my old thesaurus. In contrast to Stephanie’s college roommate, I look for short, clean words. Brevity excites me. Mem Fox said, “One-syllable words, like a good man, are hard to find.” I use my rhyming dictionary often too, finding inspiration on those dog-eared pages! Recently I offered to lend these books to my daughter as she worked on a poetry assignment, but she just smirked. The same tools are available to her on line. I decided to try her approach while I was working on a poem for my Stanford class. I stumbled on an interactive word map/visual thesaurus.
I love the free association, intuitive dynamic. Language is rich with nuance. Try this out!