Decide how you'll distribute your ebook. Where you distribute will affect your layout decisions so it's best to make these decisions now. The primary choices open to the self-publishing author are: your own website, Smashwords (along with all the distribution channels they offer), and Amazon Kindle.
Edit your book. Enlist the services of a good copy and content editor to ensure your book is the highest possible quality.
Design your cover. Hire a graphic artist to design a cover for you, or use a graphics editing program such as PhotoShop or GIMP (available free online) to design your cover. Ebook covers are much simpler than covers for print because you don't have to worry about page count and paper thickness to determine a spine width, as you do with print books. It's just a front cover image mainly for aesthetics.
Convert your book to PDF. You'll most likely want a PDF version of your book if you'll be selling from your website. If you've created your book in OpenOffice (available free at Openoffice.org), you won't need a separate PDF maker. Click "file," and "export to PDF." For ebooks your PDF won't require any specific formatting, so design and lay out the book in the way that looks most attractive to you.
Format for Smashwords. Smashwords.com is a good choice for getting your ebook distributed. Not only do they allow you to distribute your book through their site, but they can get your book into distribution with Sony, Shortcovers, barnesandnoble.com, and Amazon. They are working to expand their distribution channels further. Smashwords has a tutorial to guide you through the formatting process allowing you to easily get your book into several e-formats.
Format for Kindle. If you elect not to publish on Smashwords, you'll want your book at least on the Amazon Kindle. Amazon has a tutorial to guide you through the layout process for Kindle.
Upload to your website. If you'll be selling from your site, go to e-junkie.com to set up a simple and affordable shopping cart interface. You won't need a merchant account to sell this way since they have multiple payment options including Paypal and Google checkout.