Use “Advanced Search” to build your searches. Put each concept into its own search box.
Use quotation marks when searching for specific phrases.
If you're not getting back enough results, add synonyms or related terms to each box using “OR.”
If you can’t think of additional keywords, do a general Google search for your term or use the database's thesaurus or index to find related terms.
If you're getting back too many results, use the database thesaurus or subject index to search for the most relevant results. You can also add an additional concept to your search. Consider focusing on a particular population or more specific aspect of your original research question.