You must have a deep understanding of Java, the Android SDK, and their design patterns, and be well-versed in Android Studio and its suite of tools.
You must have the ability to successfully coordinate the work of other developers in the team and collaborate with UI/UX designers, in order to develop solid apps that will perform flawlessly under all circumstances.
Since the apps you will be working on will be used by millions of people, careful memory management and performance optimization techniques, as well as considerate resource consumption, are a requirement.