At every step, first agree on the result. Then give the agent the task, check the effect, and record the decisions in project files. If something does not work, fix that part before moving on.
Use your own idea, or a simple example: an app for saving ideas. At first it is enough to save an idea and find it after reopening the app. Add sign-in or a server when they prove necessary. In prompts, replace text in square brackets with information about your project.