I started doing the video tutorials on the Apple website. I did "Getting Started with Garageband," and "Building a Song." The videos are excellent and a further testament to the Apple production machine. They really have a good thing going.
The problem I am having is that there is too much. As a person with ADD, this is like crack for me! There are so many loops and possibilities to create songs. Pick your genre and mix it up because that is exactly what I am doing. It is fun, but I haven't made anything worth keeping yet.