Follow a real task.
Walk through a complete task with the people doing it. What starts the work, what information is needed, and where does it get stuck? A useful product brief begins with these relationships.
Make the boundaries clear.
Agree which part of the workflow the first release will improve, what remains in another tool, and which integrations are essential.
Review the working product.
Use a prototype and a small first release to test the experience. Feedback from actual users helps refine the workflow before adding more complexity.
