Use a couple key terms about your topic to try searching without keeping track to see whats out there. This is also a good time to search for already existing reviews on your topic and see if something similar has already been completed. After doing a preliminary search in your general topic, you can begin thinking about your specific research question.
To start drafting your research question, it may be helpful to consider how your topic fits within a couple of different broad overlapping fields of research. For example, the research question illustrated below asks about identity perspectives from Asian American students in high schools. Each individual topic in this question is its own circle, and the intersection of these circles is the main focus of the literature review. There could be more circles added for each new dimension I would like to add to my research question whether it be a location (i.e. New York City), a clarifying detail (i.e. generational identity), or other form of context.
As you are searching, use the different dimensions of your research question to find individual areas of research, For example, I may want to look at the literature around just the identity of Asian American students, or maybe just look at identity formation in High School. Then, in my literature review, I can synthesize these various fields to explain the different backgrounds and how they all converge around my central topic, the middle of the diagram.
Image from Tips and Strategies for Writing a Dissertation Proposal on Ashe Grads blog.
Once you have your research question and key terms from that research question, you can start your formal searching process. In narrative literature reviews it is less important to be comprehensive in checking every possibly relevant result, but more focused on making sure the results you are getting are representative of the fields you are analyzing.