Having a well defined topic will make it much easier to evaluate the search result. Don’t underestimate this step! You will likely adjust your topic at a later stage but you will save a lot of time thinking this through carefully from the beginning. It usually helps a lot if you define your research topic as a question.
Start with reading an overview, for example a textbook, a subject specific encyclopedia or a review article. Think broad. Wikipedia is ok to get a general introduction to a subject, but do not cite.
If you are uncertain about whether your research question is suitable for the task at hand, talk to your teacher or a researcher within the subject about whether the subject may be too broad or narrow. There is always a balance between finding a topic that is well established but perhaps too broad or uninteresting, and a topic that is very new and exciting but where there is very little research published.