Here is my quick checklist to ensure you’re ready to hit the ‘publish’ button.
You’ve had a Structural Edit of the book. This means that someone (preferably a professional, but if not – someone with a very good eye for these things!) has given you feedback on character, plot, structure, theme – basically all the big stuff. You’ve made changes and are happy that the story is as good as it can be.
You’ve had opinions from multiple ‘beta readers’ you trust. You don’t have to agree on all their points, but it’s good to know what kinds of comments you can expect from readers before they start leaving Amazon reviews.
You’ve had the text proofread / copy-edited. Again, this can be by a professional, but more-often-than-not, this is just done by eagle-eyed friends.
You’ve added preliminary pages / acknowledgments / a link to your mailing list at the end.
You’ve had it converted into an eBook file and you are happy with the layout of all pages on an eReader.
eBook files are easy to switch and change if you spot typos later on, so try not to feel the pressure for perfection too much. That being said, it’s worth taking the time now to ensure your book is at a high level before making it public.