Describe the market for your book – to the tiniest detail (e.g., childless divorced women past age 50 who want to remarry). Why that demographic? How do you connect with them to market to them?
I think that there's a natural inclination among writers to want our stories to appeal to everyone. We spend so much time with our books that we genuinely believe (or want to believe) that everyone on the planet will enjoy them. Unfortunately, the real world doesn't actually work that way. Even the most famous, highest-earning authors in the world aren't universally well-liked. I know plenty of people -- big readers, too, true bibliophiles who are quite well-read -- who have never touched a book by Stephen King or J.K. Rowling. I also know several people who have a seething hatred of writers who I really enjoy.
So, knowing that my book, wherever it ends up, will probably not be universally adored, I do have to wonder: who's going to buy this thing?
I can't say I have a super-specific audience in mind. After all, I am selling a novel, not a self-help book. I expect the audience to stay somewhat wide. Still, I can guess what sorts of people will definitely not like my book. I have plenty of friends who support me and my writing but who would never be fans. That's not a big deal, really. I'm not really the ideal reader for a lot of books, either.
It does get frustrating, though, because Tagestraum is...a very specific type of book, occupying a niche that doesn't necessarily actually exist yet in any official capacity. It's a portal fantasy, a story about a normal guy being pulled into a fantastic world, but unlike other portal fantasies, that world doesn't need his help to survive. There's very little romance, my lead character is a guy, and I'm writing for an adult audience.
On days that I'm feeling cynical, that right there is enough to make me think that there's no market for my book. Which is really bad, because all of the stories I'm interested in telling have similar problems.
At the end of the day, I write books that I want to read. I am my own ideal reader. So if these genres aren't selling...well, that's double-bad news for me. Because that means I won't have much to read, either.
Anyway. That's only how I feel on cynical days. On other, healthier self-esteem days, I to back to thinking that everybody in the whole world will read my book and love it, godammit.