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.
Tip
You might be wondering, what should I do? Keep making apps and don't let the lack of design experience and knowledge stop you! Even release your apps on the app store. Keep in mind, however, that there is an entire other topic, design, that needs some attention if your apps are going to truly be world class.
In medium-sized development companies, the designer is rarely also the programmer, and even very small companies will often outsource the design of their app (or designers might outsource the coding).
Designing is both art and science, and Google has demonstrated that they recognize this with really high-quality support for both existing designers and aspiring new designers.
Tip
I highly recommend you visit and bookmark this page: http://developer.android.com/design/index.html. It is quite detailed and comprehensive, and it is totally focused on Android. It also has a digital ton of resources in the form of images, color palettes and guidelines.
Make understanding the design principles your short term goal. Make improving your actual design skills an ongoing task. Visit and read design focused websites and try and implement the ideas that you find exciting.
Most important of all, however, don't wait until you are a design expert to make apps. Keep bringing your ideas to life and publish them. Make it a point to make each app a little better designed than the last.
We will see in the coming chapters, and have seen already, that the Android API makes a whole bunch of super-stylish UI available to us that we can take advantage of with very little code. These go a long way to making your apps look like they have been designed by a professional.