In any kind of business the first step that you must always consider is to identify your market. The selling part and the marketing part can be done at the later part, you must prioritize your market first. Once you establish your market, the rest will just follow.
Consider selling a ebook. It is not enough just to know how to create an ebook or write about something you should know. These factors are important in creating an ebook, but these could not be a determining factor that you can sell it right away. Just because you have a knowledge about the topic doesn’t mean you can sell your ebook. Focus on your target market and you will get good result.