Search terms will depend on your topic of course, but generally you will want to use the most important words related to your topic or what we call keywords.
Keywords may be terms you already know and use to describe your topic, but it may be helpful to look at some background information by looking in a related textbook, reading reference sources, or searching the web to find out what words are being used to describe this issue.
Brainstorm related words to the main keywords you have in mind, like synonyms, or words that have the same meaning. Some sources may be using different words to describe the same thing.
Check out the Thinking Tool linked below, and the video on how to use it for a step by step process that can help you refine your topic and come up with keywords.