What do you want from your book?
How much time, money, and effort are you willing to invest in it? You might simply want to publish the novel you’ve been working on for a decade, and have no interest in selling actual books (perhaps you’d rather start writing your second novel). Thanks to print-on-demand, that’s a viable goal.
Like many indie authors, I wrote my book without a business plan, because I wasn’t thinking of it as a business. I wrote my book because I had stories to tell, and published it because I could. Only after the fact did I consider actually selling books. That’s a fine approach for people who aren’t planning on selling a lot of copies, but it’s a poor strategy for anyone who is writing as a business.
At the other end of the spectrum, you might know ahead of time that you want to do whatever it takes to make your book into a bestseller. (Hint: It usually takes a lot of money.) Excellent organization, thorough planning, a savvy agent, a big-name publisher, a powerful story, skill and experience at storytelling, a publishing track record, great connections, famous friends, an interesting backstory, and the assistance of an experienced marketing or PR professional are also helpful. (Some politicians have “created” bestsellers by buying up thousands of copies of their own books and then giving them away to campaign donors as thank-you gifts.)
Deciding what you want — and what you’re willing to do to get it — is the first step in developing your marketing plan.