Use the Advanced Search options - particularly the Publication Date setting
Try searching for words that would have been used during different time periods:
"Color line" instead of segregation
Indians instead Native Americans
Negro or colored instead of African American
"Lunatic asylum" instead of "mental hospital"
Use the asterisk (*) to search for variant endings:
immigra* searches for immigrant, immigrants, immigration, immigrate, etc.
suffrag* searches for suffrage, suffragist, suffragette, etc.
Use quotations to search for exact phrases:
"League of Nations"
Use AND between search terms to look for all the words:
marriage AND morality
electricity AND invention
Use OR between similar words to search for either term, but not necessarily both.
law OR act OR legislation
"lunatic asylum" OR "insane asylum"
Use NEAR/n to search for two words or phrases within close proximity (ProQuest newspapers only):
war NEAR/6 veterans
natural NEAR/4 environment
Combine search tools to create advanced search strategies:
Eugenics AND (population OR "birth rate")
Religio* NEAR/5 "public schools"
Be creative in trying different terminology and combinations! Searching is a process of trial and error. Not everything you try will be effective and that's okay. There isn't one "right" search strategy to find everything that you want.