If you want to sell your book, you have to do several key things before you write the first word. These have little to do with the quality of your writing and everything to do with the purpose of your writing.
The very first one is to ask yourself who you are writing to. This is your audience, your target market, or whatever else you choose to call it. Who represents this market, what do they want, what to they need, what do they fear? Be very certain who you are writing to before you write the first word.
Second, ask yourself what they know. If you write too advanced a book for your audience, they will not read it. If it is too general or too simple, again your audience will not read it.
Third, ask yourself what you want them to know after they have read your book. This does two things. It gives you an end point but it also tells you what you have to build up to as you write. The chapters you create will be the steps from what your audience knows to what you want them to know. You can’t decide what to put in the chapters unless you know this.
Now that you know who you are writing to, your writing has purpose. When it comes time to market your book, you will know which organizations to speak to, how to position your marketing materials, what radio shows to get on, and where you will find your email list and social media followers.
By deciding these three items, you have already started to market your book. Good luck!