Name the person and the problem
Be specific about who the app helps and the problem it solves. Describe the current workaround and why it falls short. Your first audience does not need to be everyone; a focused initial group makes it easier to decide what belongs in the first release.
Choose the smallest useful release
Map the essential user journey from entry to a completed task. Build the features needed for that journey first. Defer optional dashboards, complex rewards and additional user types until the core experience is useful and reviewable.
List operational dependencies
An app may need payment accounts, map services, SMS providers, video hosting, content and store accounts. Identify the owner of each dependency early. Availability, usage limits and recurring costs can affect both the timeline and the architecture.
Plan the day after launch
Decide who answers customer questions, manages content, reviews problems and approves updates. A launch is a transition into operations. Including these responsibilities in the brief makes the product easier to run as real users arrive.