Use this worksheet to help you figure out key search terms based on your research question/thesis!
Look at your results, what terms are popping up? You might not have phrased it like that, but maybe that is what it is called in the literature.
If there's a thesaurus tool available, use it! PsycINFO's thesaurus tool is invaluable! Also be sure to look at an article's subject terms or author supplied keywords.