Determine whether the database considers multiple words as a single phrase, or a combination of words connected by OR (any of the words) or AND (all of the words). Ex. Academic Search Complete's default search is a phrase search (less results) - put each word into a seperate box to get more results.
Use truncation symbols. Each database has its own truncation symbol (*, ?, $, #, !). Ex. engineer* will retrieve engineer, engineers, engineered, engineering, etc.
Use controlled vocabulary (or subject headings, descriptors, thesaurus) to ensure that items being retrieved are specifically on the topic of interest.
Use refine results features to narrow down results. Refine by document, publication, or literature type OR add terms like "survey paper" or "overview" into a keyword search box to find review articles.
For more tips on selecting and using databases, see the Databases guide.