Strategies:
Use a wildcard * for word variations.
Example:
slave* will retrieve slave, slaves, slavery, slaveholder, etc...
Quotation marks force words together into a phrase:
Great migration might retrieve articles about great grandparents and migration, or the great war and migration.
"Great migration" in quotation marks would refer to the specific phenomenon of Black Americans moving from south to north during and after World War 1.
Use advanced search to structure your topic
Consider the different dimensions of your topic: who, what, where?
Example: What role did African American women play in the great migration in Boston?
Who: african american women, Black women
What: great migration, northward migration, Black migration
Where: Boston, Greater Boston, Beacon Hill, Roxbury, North End
See a tutorial for more examples of this strategy.
Use the "peer reviewed" filter when you want scholarly peer-reviewed articles

Consider outdated vocabulary when searching for historical documents of the past:
Example:
african american OR black OR negro etc...