Scholarly databases usually have multiple search boxes.
Break your topic into keywords or very brief phrases and place them in separate boxes for best results.
Be flexible with your search terms. If your first combination does not yield useful or relevant research, change up your terms and try again.
As you browse search results, be on the look out for new terms and vocabulary to try.
Keep track of the terms you've used and the databases you've searched to insure you do a thorough job.