This is the approach that was taken for developing the formal Release 2 test plan. Sit down and think through all of the things that you do in the course of an academic year. Use this list to monitor what you actually do for several days. Record anything you left out the first time through. You might also want to distribute your list to others for them to review.
Several heads can be better than one.
Ask what they are doing and why whenever you see something new. Make a list of all the screens that the person accesses and a brief description of what they are using the screen to do. You might want to work out a schedule where you would spend a few minutes with them whenever they started a new task. Have the person you interviewed review the list for completeness. Be sure to include seasonal activities related to the academic year.