Do some "pre-search" by reading about your topic in a reference source or textbook.
Wikipedia can be a great resource at the early stages of research. You can use it to identify vocabulary for your keyword searches, give you some background information, and point you toward scholarly sources and reporting on your topic.
Look at the subject tags on your search results to identify additional search terms.
You'll find these under the search result in most databases, and on the item page.
Use database thesauri and subject heading lists.
Many databases have standardized lists of terms, or a "controlled vocabulary," for consistent subject labeling. You can keyword search these to find the best search terms for your topic.
In EBSCO databases, look for a link to a thesaurus or subject heading list in the blue ribbon menu across the top of the page.