In library databases use key search terms that express the most important concepts related to your topic.
The more terms you use the fewer results you get, so be selective.
Example: A search like impact of gender on people's salary expectations will get far fewer results than gender AND salary AND expectations.
Brainstorm terms that mean the same thing.
Example, an article about salary may not use that word, so try terms like wages, pay, income, or earnings. Searching for all of those terms together with OR between them (example: gender OR pay OR wages OR income OR earnings) tells the search engine to find at least one of the terms in your search results.
Quick background research may help you identify effective keywords.
See resources in reference databases like Gale Virtual Reference Library and Oxford Reference Online which contain general and subject-specific resources (e.g. Business, Education, Psychology.) Wikipedia may also provide basic information about your topic (e.g. keywords, people's names, or place names). Once you have your key search words, try them in various combinations in the library's research databases.
Brainstorming Keywords Video (Portland State University)