Start right here:
Getting Started | Android Developers.
The Android Developers site is your best friend. It even includes the instructions for installing and setting up Eclipse, the ADT plugin, the JDK/JRE, etc. Every training session, every tutorial, and every code sample will be relevant and helpful to you, trust me on that. I still refer to those guides and examples every few days because they're well-written and a good base for approaching problems. Build the applications from scratch; don't copy and paste code, even if you know exactly what it does and how it works.
The
Android Design Guidelines go over Google's vision for Android and its applications ? everything from their creative vision and design principles to specific colors, fonts, and icons to use.