When you find a relevant book or article, make sure to look at the subject terms listed. Think of these as hashtags on Instagram. You can then look for articles with those subject terms to find other potentially relevant items.
When you find a useful book in the library catalog, look at the record's Library of Congress Subject Headings, which are hyperlinked in blue. Click on one to discover other similarly tagged items or use the headings to give you ideas for terms you can try in a keyword search.
Though it's recommended to focus on the hyperlinked subjects listed in relevant articles first, databases also have tools to help you discover the subject terms it uses to tag articles. For example, most EBSCOhost databases have a thesaurus link called Subject Terms above the search box.