Pick out the key concepts (usually nouns) that make up your topic, and omit common words like: what, the, is, of, have, etc. For example, if your topic is: What is the survival rate of prairie dogs that have been relocated? You should only search for the words survival, prairie dogs, and relocate.
Brainstorm synonyms for your main concepts.
Synonyms are terms that mean the same or similar things. Let’s say you are investigating the relationship between income and gender. Just because your research topic uses the word income does not mean that every author uses that same word. Some authors might use synonyms of income, such as wages, pay, salary, or earnings. In order to collect all the relevant articles on your topic, you might want to include these synonyms in your search.
Combine concepts and synonyms with AND, OR, or NOT.
AND narrows or restricts a search. Entering survival AND prairie dogs AND relocation tells the database that it must find sources with all of those terms. The more concepts you enter, the more you are restricting your search.
OR broadens a search. Entering survival OR mortality will retrieve sources with either term. Use OR to search for multiple synonyms in a single search.
NOT narrows your search by excluding items. In the gender and income example, we might want to say gender NOT race.
Find additional keywords to try in your searches.
Conduct Google or Wikipedia searches on your topic, then scan for keywords and synonyms. You can also find additional keywords by doing some preliminary searches in a library databases.