Once you have a general topic in mind, brainstorm 5-10 related search terms BEFORE you start your research. This will help you define your research question.
For example: Search terms for Racial Inequality could include specific instances of inequality between races such as incarceration rate(s) or wealth disparity.
Search terms for Immigration could include related words or terms like refugee(s), undocumented, or DACA.
Search terms can also include names of people, events, or places: while researching Climate Change you could use terms like Greta Thunberg, Paris Agreement, or Hurricane Ida.