Amazon's Kindle Direct Publishing (KDP) is the closest thing to a public utility for self-publishing books. Anyone can put a manuscript and a cover into it, and within about 72 hours you have a book for sale, in print and on Kindle, in dozens of countries. That accessibility is amazing. It is also why most of the books on KDP are bad.
I've put four books through KDP under two names. Some sold reasonably; some sold three copies, all to my mother. Here's what I learned, in the order I wish I'd learned it.
The manuscript is the easy part
If you can write a book, you can format a book. KDP accepts a properly formatted Word document for both Kindle and paperback. There are templates. They work. You do not need Vellum or Atticus or InDesign for your first book; you need a manuscript that has been read by a human who is not you.
The non-negotiable steps are: spell-check, a real proofread by someone else, and a print proof copy that you read on paper before you publish. Typos that are invisible on a screen are obvious in print. Always order the proof.
The cover is the marketing
On Amazon, your cover is a thumbnail roughly the size of a postage stamp. Most decisions to click are made at that size. If your title is unreadable at thumbnail scale, your cover is wrong, no matter how nice it looks blown up.
Look at the top-selling books in your category. Note the dominant color, the type style, the way the title and author name are arranged. You do not have to copy them, but you do have to look like you belong on the same shelf. A cover that screams "I made this in Canva in twenty minutes" tells readers your book is also a twenty-minute effort. (Even if you did make it in Canva — and you can — give it more than twenty minutes.)
Pricing: lower than you think for ebooks, higher than you think for print
Kindle pricing has a sweet spot between $2.99 and $5.99 for most genres. Below $2.99, you drop from a 70% to 35% royalty rate, which is a big cliff. Above $5.99, you start losing the impulse-buy reader. There are exceptions, but if you don't have a strong reason to deviate, start in that range.
For paperback, the price floor is set by Amazon's print cost plus a minimum royalty. A 200-page paperback will probably need to be priced around $9.99 to $12.99 to give you any royalty at all. That's fine. Print buyers are not as price-sensitive as ebook buyers.
Categories and keywords matter more than you think
KDP lets you pick categories and keywords during publishing. Most authors pick the obvious ones and stop. Don't. Pick the narrowest specific category your book honestly fits in — being #1 in a small subcategory is far more useful than being #4,000 in a giant one. Use all seven keyword slots. Think about what a reader would actually type, not what you wish they would type.
After publishing, you can email KDP support and request additional categories beyond the two you picked in the form. They'll usually grant a few. Most authors don't know this and leave free real estate on the table.
The long tail is real, but slow
Most KDP books do almost nothing in the first month, then settle into a baseline of one to a few sales per week, indefinitely. That baseline can last for years. Four years in, my book of really bad poetry — written entirely as a joke under a pen name — still sells a copy or two a month, to total strangers, for reasons I do not fully understand.
Don't measure success in the first thirty days. Measure it over a year, and across your whole catalog. The second book sells the first book. The third book sells the first two. This is the part the gurus undersell because it doesn't fit in a launch-week screenshot.
What I'd do differently
Start with non-fiction in a clearly defined niche. Fiction is harder to market because readers don't search for it the way they search for "lean management examples" or "wedding speech templates". A non-fiction book that answers a specific question is easier to find, easier to position, and easier to price.
Build an email list before publishing the next book. I haven't done this and I regret it every single launch.
The actual barrier
The barrier to self-publishing on KDP isn't technical or financial. It's that finishing a book is genuinely hard, and the system rewards people who finish more than people who plan. If you've got a manuscript sitting in a folder, the most valuable thing you can do this week is open it.