Choose one useful outcome
Begin with the main task your app will help someone complete. A planner might help organise a day; a tracker might help record a habit. Describe the outcome before writing a long feature list.
Sketch the core journey
Write the steps from opening the app to completing that task. Think about what users enter, what they see next and how they know the task is complete. Simple sketches are enough for an initial conversation.
Identify what the app depends on
Explain whether the app needs accounts, internet access, notifications, payments or another service. Also consider what should happen when a connection is unavailable. These decisions influence the scope and implementation.
Create a launch list and a later list
Keep features that are essential to the main task in the first release. Put optional refinements in a separate list. This makes it easier to agree a realistic first phase and learn from its use.
Define how the work will be reviewed
Agree the target devices, important user journeys and delivery format. Decide who will provide store information and manage publishing accounts. Release preparation and ongoing maintenance should be discussed as part of the quote.