Filters or facets: allow you to narrow your results by source, subject, date range, etc.
Wildcards: in many search engines, the asterisk is a truncation symbol that will match all possible endings for a word stem; i.e. histor* will match history, historical, historicism, historiography, etc.
Booleans: combine search terms using AND (gender AND identity), OR (black OR african american) and NOT (shanty NOT sea).
When you find a good source, use it to find other good sources. Use the subject terms and keywords associated with an item to find other items on the same topic. Scholarly books and articles will have bibliographies and footnotes that you can mine for additional resources.