The first question to ask yourself before you write a book is: what is my goal? If your goal is to simply write a book. Great begin at the beginning and go. But if your goal is to sell a book then the following are things you need to know before you write that book.
1) What genre is your book? By this I mean, if you were to go into a bookstore and find your book, what shelf would it be on? If you don't know what shelf, you will struggle to sell your book. If you think it could go on multiple shelves, you need to rethink your idea. Booksellers need to know where your book goes. Edit it down to one shelf.
2) Read other books on that shelf. To truly understand where your book goes and why, you need to read, read, and read the other books on the shelf. Look for trends. Keep in mind the books you read today were on editors' desks two years ago, so that hot vampire book might be too cliché by the time you get it written. I chased trends for years before I sold my first book. The key is to read more than bestsellers. Read broadly.
3) Pay attention to who else is reading the books on your shelf. Are they young? Are they old? Do they like metal music or country music? Where do they talk to other readers who read the same thing? Go there and listen to what they say about the books they love. Your first draft is written for you, but in order to sell the book, you need to write it for readers. Keep in mind their expectations, wants, and needs.
4) Find out what publishers, editors and agents want to read a book like yours. You can look at the publishers of works on your shelf. Check out the acknowledgments for mentions of editors and agents, check out websites like https://pred-ed.com/. Stalk the publisher and agent websites and find out who is looking for your type of book and what they would need in order to buy it.
If you've done these four bits of homework, the next step is to write that book. You can't sell it if you don't finish it. Need a guide on your writer's journey? The Write Advisor is here to help. Sign up for your free 15 min zoom call to see if our service is right for you.