Other than a chosen few best-selling authors, the people making the most book-related money are those that offer promotion services, teach classes, or provide other publication help, such as cover design, formatting, and video trailer creation.
Unless you have unlimited resources, choose them wisely to make sure you get your money’s worth and a suitable ROI (return on investment). While any new endeavor requires a certain level of investment, it’s an easy trap to fall into where you’re putting out far more money than you’ll be able to recover for a long time. Making easy money by becoming an author is about as likely as becoming a famous singer or Hollywood star. The odds are not in your favor.