The apps that retain users are the ones that found a clear job to be done and refused to add scope until they had done it well. We run product definition as a formal phase: user research, journey mapping, prototype testing and a functional specification before a development sprint begins.
The build follows on native iOS and Android, with a marketing and ASO programme running in parallel so the App Store launch lands in an audience rather than a void. We stay involved post-launch, because the first version is a hypothesis, and the data from real users is where the real design begins.