Facets: Most databases will allow you to filter your results using "facets" (sometimes called limiters or refiners). These are the options (normally located on the right side) that allow you to only display results that meet certain criteria such as peer review, full text, year of publication, etc. Using facets can really help to cut down the number of results you get from a search.
Bibliography Scanning: When you find an article you like, look at the bibliography. There is a good chance that you will find other articles that would be helpful to your research.
Find Alternate Keywords: Often databases will list the keywords that are associated with the article you find. You can sometimes find this information in the abstract of the article as well.
Boolean Operators:Use of Boolean operators (AND, OR, NOT) can sometimes be useful to help tie together or separate search terms. Use AND to only find articles that contain both of the keywords you're looking for, use OR to search for articles that use either one, and use NOT to eliminate a search term from your search.
Truncation and Wildcards: Root words can have multiple endings Example: sun = suns, sunshine, sunny, sunlight. Likewise there are some words that are spelled differently, but mean the same thing. Example: color, colour
Still confused on how Boolean Operators work? Try out the Boolean Machine.