Unless you are a Stephen King or a J.K. Rowling, you might be doubting the possibility of "giving up your day job" and becoming a full-time author. Let's face it, most books don't sell very well and those that do usually just make the author enough to supplement his or her income. I am here to tell you that if you do have one (or more) of those books that do sell well, perhaps making you around a few hundred dollars per month, you can capitalize on that success and turn that additional income into a much greater amount. You do this by expanding your product offering.
So why must you start with a decent-selling book? Basic math. Zero time zero is still zero. Or to put another way, if you base an entire product line on a crappy product (granted, your book might be awesome, but it is crappy-selling) then what you will end up with is an entire product line that doesn't sell.
If you do have a decent-selling book, you should have already considered the other common book formats, including paperback, hardcover, and audiobook. This is a quick and easy way too often triple what you are currently making from an ebook alone. Do keep in mind that all books do not always work in all formats. For example, a coffee table photo book does not work as an audiobook.
So here are just some ways you can expand your product offering and get closer to being able to be a full-time author.
This is just the tip of the iceberg. Depending on your book, your talents, and your creativity, there could be many opportunities awaiting you. Keep thinking!