What should new authors know before they publish a book online?

[ackerman]

I'm preparing my first book and exploring how to publish a book online without making costly mistakes. What steps should a new author follow, and which options are worth comparing? I'm especially interested in formatting, ebook platforms, ISBNs, pricing, distribution, and royalties. How can I avoid hidden fees or poor agreements? I'd appreciate serious, honest advice from authors with recent experience publishing online.