Research is an iterative process, and sometimes your search phrase doesn't work like you thought it would. When this happens there are two strategies you can employ:
When you get zero (or very little) search results > Broaden.
Usually very little search results is caused by a search phrase that is much too specific. It is also possible that very little has been written on your topic, or you are using the wrong database for your topic area, but it is usually best to begin fixing this problem by broadening your search phrase.
When you get too many (or irrelevant) search results > Narrow.
Usually getting too many search results (more than 2,000) is due to your search phrase being too vague or too broad. Below is an example of how to narrow a search using multiple methods, Try only one of these methods at a time, re-running the search each time so that you can find that sweet spot of not-too-narrow and not-too-wide.
And as always, feel free to rech out to your librarian for help in building search phrases.