Don’t write your book to appeal to a “market.” That’s like aiming for the target on an archery range. Instead, aim for the very center of that target: a single reader.
Aiming for the center is critical to writing a great book. It’s like archery. Aim for the target and you may miss. Aim for the center of the target and you’ll probably hit the target, even if you miss the center.
The center of your target is a single reader, one with a name and a history and habits. I often ask clients to pick a person they know who is the ideal target reader for their book. Then write the book as if you were writing to that one, specific person.