Chapters 1-3 in Sagor provide an overview of the whys and hows of teacher inquiry/research.
We will be working through the processes he describes, so don't worry if they are not clear to you right now. The first step is "finding a focus" (p. 12). Without overthinking, what are some issues/problems that you could see researching? These could be big picture issues about pedagogy, such as grading, for example, or they could be one kid or a small group of kids who are having specific issues in your class, either academically or behaviorally.
Why are these issues important to you? When did they arise?