App design is a vast topic. It is a topic that we could only begin if it is taught in a book of its own. Also, like programming, you can only start to get good at app design with constant practice, review, and improvement.
So, what exactly do I mean by design? I am talking about where you put the widgets on the screen, which widgets, what color should they be, how big should they be, how to transition between screens, the best way to scroll a page, when and which interpolators to use, what screens should your app be divided into, and much more.
This book will hopefully leave you well qualified so that you are able to implement all your choices of the preceding questions and many more besides them. This book unfortunately doesn't have the space and the author probably doesn't have the skill to teach you how to make these choices.