I’ve been asked many time to explain how I’ve learned Android Development. And I’ve always answered that the official ressources on the Android Developers site associated with the “Professional Android 2 Application Development” book have been perfect for me.
But here is the nearly perfect blog post you should read : Getting Started with Android Development, by Jean Hsu.
And to begin with, got to the Android SDK download page.
edit: fixed URL, added direct link to SDK download page