I just read a very clear  explanation of the economics of publishing by a successful author, here. Make sure you read the comments, too. If you don’t understand what advances and royalties are and how authors are paid, make sure you read Joe’s explanation.

(This applies to traditional publishing.  Some of the newer publishing models are different. With Intermedia, for example, there are no “royalties” per se, you pay for their services, for instance, if they act as your distributor or fulfillment house. And they pay your share of sales every month. For more about publishing and Intermedia, go to www.askaboutpublishing.com. You can even ask a question there.)

It is difficult to make a living as an author, from a book alone. One thing that helps is becoming prolific. I taught a class on this once, and you’re welcome to check out the replay and notes for Writing Secrets Revealed. When writing becomes almost as natural as breathing, you have a better chance of putting out several books a year (and don’t forget spinoff info products that can be more profitable than a book).