To choose a business book idea, start by writing your book promise. That’s one sentence that spells out what your reader has when they finish your book, who the book is for, what won’t be in it, and what you want the book to bring into your business. Once you can write that sentence, it gets a lot easier to see which of your ideas is the book you should write first.
Holly Haynes asked me about this when I was on her Crush the Rush podcast, because she wanted to know what someone could do this week if a book had been on their to-do list for years. My answer was to write the promise first, since about 80% of the people I talk to skip that step.
What usually happens instead is someone says, “I’m really good at marketing, so I’m going to write a book about marketing,” and then starts pouring in everything they know about marketing. That doesn’t work, because without a promise there’s nothing deciding what goes in and what stays out, so the book ends up as a lot of spaghetti thrown at the wall. A book that delivers one thing in a strong, solid way does a lot more for your reader (and for you).
If you’re not sure yet which direction fits your business, my free Strategy Stack quiz can sort that out in a few minutes.
What Goes into a Book Promise
Your book promise works a lot like a subtitle, in that it spells out exactly what your reader has when they finish reading. I have my clients write it before they outline, title, or draft anything, because the promise is what tells you which stories belong in this book and which teaching can wait for a different one.
When I walk someone through it, we answer four things:
- What you’re delivering to your reader, meaning the specific result they walk away with, said in words they’d actually use
- Who the book is for, which works best when you can picture one specific reader
- What won’t be in the book, because writing this down is what keeps one book from quietly turning into three
- What’s in it for you, meaning what you want the book to bring into your business
Authors skip the fourth one more than any of the others, and I understand why, since it can feel a little selfish to write down what you want out of your own book. But every book makes a promise to the reader and a promise to the author. When you have both written down, planning gets so much clearer and the writing goes so much faster, because you aren’t stopping in the middle of every chapter to decide whether something belongs.
To give you an idea of what this looks like, a grief counselor writing about the first year after losing a parent might promise readers a plan for that year, including the birthdays and holidays that tend to hit hardest. Estate planning and legal paperwork would stay out, since those belong in a different book, and the counselor’s promise to themselves might be getting invited to speak at hospice organizations in their state.
Once you’ve written yours out as a sentence, you’ve taken a bigger step than it looks like on the page.
How to Narrow Down Your Book Ideas
The first thing I look at with clients is what they want to be known for and what they’ll still enjoy talking about three, four, or five years from now. A good book should keep bringing you leads for 5 to 10 years, maybe longer, so it doesn’t make sense to write about something you’re planning to move away from next year.
People often come to me with three ideas, where one is pretty broad, one is super niche, and one sits somewhere in the middle. All three are usually good ideas, so the question I end with is which one they’re actually excited to write.
If none of your ideas feel exciting yet because they’re all swirly and chaotic in your head, that’s completely normal, and it’s what my bookigai exercise is for (it’s named after ikigai). You brain dump everything you might want to write about, and then we go through each idea and look at how well it lines up with your business goals, your Strategy Stack, and what you actually want to spend your time on. Sometimes we find out there’s a second book in there, too, and in that case the first book goes super specific while the second one can go broader later.
The bookigai is included in my free guide, What’s Working in Books in 2026, which I update every year so it’s current whenever you find it.
The Five Doors a Business Book Can Open
The authors I work with usually come to me wanting their book to open one of five doors for their business:
- More clients
- More paid speaking gigs
- More passive sales, like digital products, memberships, and courses
- Thought leadership, so you’re known for what you know
- Partnerships, like corporate or nonprofit partners, or your book being used as a textbook or in a university course
I call these Strategy Stacks, because you can stack them on top of each other. If you write your book to get more clients, it can still bring you speaking gigs and partnerships later on, but one door leads and the whole book gets planned around getting your reader through that one.
You could dump all your thoughts into a row, put a table of contents on top, and publish it. Aiming the book at one door is what decides your promise, the order of your chapters, the stories you pick, and what you ask readers to do when they reach the last page.
Aiming your book also affects what it earns you. The Business Book ROI Study collected data from more than 350 business authors across traditional, hybrid, and self-publishing. It found that authors with a clear strategy for their primary revenue goal typically made a profit of more than $96,000. Royalties are the smallest piece of that, and I broke down the bigger pieces in all the ways to make money from your book.
Your Title Has to Point at the Right Book
It’s easy to treat your title as a small detail, but your title and subtitle have a lot to do with how well your book sells. If they don’t match the book you actually want to write, you can end up writing the wrong one.
Say you start a book called Marketing 101 with the subtitle How to Be an Online Marketer, which already describes two pretty different books. Then you get halfway through and realize the only marketing you really like teaching is Instagram marketing. So the book isn’t Marketing 101 anymore, and half of what you’ve written belongs to a book you don’t want to finish.
This is the kind of call I help authors make in the Book Bestie™ Hotline. You send me your book ideas, your promise, and the title you’re considering in Voxer, by voice or text, and I get you a real answer about your book within 72 business hours, so you know you’re writing the right book before chapter one. Check the Hotline page for current pricing.
Your Promise Decides Which Book Gets Opened
Books are a strange mix of product and art. People buy nonfiction a little like they buy toothpaste: it doesn’t matter much whether it’s Colgate or Crest, because they just want a marketing book. So they’ll often buy two or three that look good and decide later which one to read. Once they’re reading, though, they care a lot, the same way you’d care if you bought a ticket to Super Mario Brothers and ended up sitting through Moana 2.
That means selling a $10 ebook or a $20 paperback isn’t the hard part. The real sell happens at home, when those books are sitting in front of someone and they’re deciding which one to open first.
When they choose yours, they’re giving you their time, which is worth a lot more than the $20 they spent, because they’re about to spend 8 or 10 hours with you, maybe more. They’re basically saying, “I’m ready to be convinced. Just treat me right,” and you didn’t have to beg them to watch a single reel to get there.
What keeps them reading is emotion, because we remember the things that shock us, surprise us, or make us feel something. I spent about five years putting the Heroine’s Journey together from story structure and research on human psychology. The whole idea is to emotionally anchor each key teaching moment in the right spot, so your reader gets to the end wanting more of whatever your promise pointed them toward.
Reader-analytics company Jellybooks considers a completion rate over 50% very good, especially for nonfiction, and fewer than 5% of the books it has tested get past 75%. That means a book that keeps readers to the end stands out. When it works, the book can start bringing in clients early. I’ve had clients sign new clients from their beta readers before those readers had even finished the book, and before it was fully published.
You Don’t Need a Big Audience to Start
You do need some audience. If you’re brand new and still figuring out your business, I’d hold off on the book, because a book needs a few people talking about it to get going. Once you have clients and a clear offer, the audience you already have is enough to start with.
A smaller audience can go a long way with a book, for a few reasons:
- Amazon doesn’t care whether you’re famous, only whether your book is selling, so you don’t need a huge email list to get it off the ground.
- Books get passed along by word of mouth a lot more than courses do, and even a copy on your coffee table does some selling when a friend visits and picks it up.
- A book written the right way keeps selling for years, which gives it time to grow and compound.
You also don’t need a blockbuster first week or to sell out like Oprah. Most successful books are in what’s called the midlist, which means they aren’t bestsellers but they keep selling steadily, and at the end of the day you make more money that way anyway.
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Write Your Book Promise This Week
If a book has been on your list for a while, the promise is the thing to work on this week. Write down what you’re delivering, who it’s for, what won’t be in the book, and what’s in it for you, and then put all of it into one sentence.
To figure out which door your book should open first, take the free Strategy Stack quiz. If you’d like help getting your promise, title, and subtitle down to the word, send me your questions in the Book Bestie™ Hotline.
PS: The whole conversation with Holly Haynes is on YouTube and Apple Podcasts. We also talked about writing in seasons, and the one book-writing rule I completely disagree with (just freewrite and see what happens).
Your nonfiction book bestie
Hi, I’m Holly.
I’m Holly Ostrout, a nonfiction book and publishing coach. I’ve worked on books since 2014 and coached nonfiction authors since 2018. I help entrepreneurs (mostly women) write one Damn Good Book™ that brings in clients, lands speaking gigs, and makes their business simpler, smarter, and more visible.
If this article resonated, here’s what to do next
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