1. What is the question my book answers?
2. Who cares? Who is seeking the answer to this question?
3. Where do I find that caring audience?
Next, you must know who cares about that question. Where is the hungry crowd who is going to be fed by your book? What do you know about them? Are they young? Old? Predominantly male? Female? Young adults? Spanish speakers? What language will they feel comfortable with? You might build a “persona,” a description of your ideal reader that covers age, gender, socio-economic considerations, education, and so on. Give that persona a name. Cut out a magazine picture that represents them, so that you can keep them in mind as you write.
Finally, you have to know how to reach those people who are going to be very interested in the answers you provide to the question you posed. Do they read particular blogs? Do they use particular search terms? Do they belong to professional associations? If you know where they gather, you will be able to let them know about your book.
Answering these questions is not optional, if you want to have a successful book. It is a prerequisite. And if you can’t answer the questions, get help. Discuss them with your friends, your colleagues, your coaches. Post a query on Quora.com; crowdsource your answers.
Do not start writing until you can answer these questions!