Name the result before the features.
A product brief can become a list of screens surprisingly quickly. Dashboard. Settings. Notifications. An editor. Each sounds reasonable, but the list still does not explain what a customer can accomplish when the product is finished.
We start with a sentence about the work. For example: an operations manager creates an approval process, sends a request through it, and sees the decision. That gives us a person, an action, and a result. Now there is something concrete to design, build, and discuss.