Choose search terms that you expect to find in written documents about your topic.
If you're looking for secondary sources (including journal articles or books written by scholars), use the language you would expect to find in a scholarly publication.
If you're looking for sources aimed at the public (newspapers, TV news transcripts, blogs), use more colloquial language when searching.
Especially when researching in political science, keep in mind that individuals with different opinions on an issue may use very different language to discuss it. For example, think about who uses the term anti-choice and who uses the term pro-life.
Here are some other ideas to consider:
Once you have found a few sources on your topic, take note of the language that is being used and incorporate it into your search.