When asked who their target reader is, many authors reply, “I do not know,” or “everybody who likes (their topic).” Either answer will reduce your sales and profits. If your book is for everybody, how much would it cost you to reach them frequently enough to make an impact -- if you could find a way to do so?  Define your target readers with the Five Ws: Who are they? What do they want to buy (printed, ebook or other)?  Where do they shop? When do they buy? And why do they buy (problem they want to solve)?