I found this great post from Author Sarra Cannon. She's an independent young adult author and has reached 100,000 sales. On her site she does a breakdown on her sales and explains how she's been able to do so well.
Check it out here.
For me the biggest lesson is the amount of material she has brought out. Her sales are strong because she has a lot of books that the readers can enjoy. Sure, marketing is important, but sales come from plenty of product. And that translates to lots of adventures for the readers to enjoy.
I've got some history on producing lots of little stories. I can do this. So watch this space. I've got some plans.