If you develop Android based application design and development you should refer the Android design guidelines authored by the official Android user experience (UX) team. It provides the basic principles to be followed by developers and specific guidelines related to devices and displays, themes, touch interface, metrics and grids, typography, color, iconography including the rules for writing user interface prompts.
The Android developer portal includes a comprehensive training resource center that helps you to learn the concepts associated with development of Android app in a step-by-step manner with the help of comprehensive explanation, flow charts, code snippets and sample projects.
If you are a beginner you should first refer the materials provided under getting started panel. After learning the fundamental concepts associated with the development of Android applications you can delve deep into the development of apps with multimedia, graphics, animation, internet connectivity, cloud computing, user info and location.
Moreover, the portal also provides the best practices to be followed for creating performance oriented apps including the measures needed to be taken to ensure security and privacy. You will also learn how to make use of Google play to distribute and monetize apps.
The developer relations team hosts a Android Design in Action live show each week where they discuss the best design concepts, guidelines and practices on the show with the help of live demos.
Pluralsight offers courses on Android development, Android 4.0 features, Android programming with intents, Improving user interaction with the Android ActionBar and Android Async programming and services.
There are numerous books available for Android application development and some of them are listed below
Beginning Android 4 Application Development by Wei-Meng Lee
Professional Android 4 Application Development by Reto Meier
Programming Android by Zigurd Mednieks
Android Programming Painless by Camilus Raynaldo
100 Ways To Use Your Android Device by Jaison B
Apress and Packt Publishing has released over dozen titles for Android development.