Determine what you earn: Now that your pricing is set, your profits are going to look absolutely fantastic. Most services now offer 60 to 70% commissions on sales, and some smaller sellers give you even more. The bottom line is that you'll be making close to $7 for each book sold, which is vastly more than you would make with a dead-tree book--often about $1 with a traditional publisher, and only after you've made back your advance (read: never). Even print-on-demand sales aren't much more profitable: The Five Stars! print version, published by Amazon's CreateSpace service, earns about $8 on each book sold for $19.99 at Amazon, but books sold elsewhere barely earn $4 each.
Understand your rights: The terms of service for ebook sellers tend to be byzantine and baffling. I won't pretend to be an expert about these terms--or even to have read them--but if you're concerned about what rights you're giving up, pay close attention to the fine print. Apple's iBooks Author terms have already generated significant controversy.
Tackle the DRM conundrum: One of the big decisions is whether to protect your book with digital rights management technology, which prevents it from being shared with other readers. DRM will lock your ebook to the reader's account and the service from which the customer purchased it. The argument over DRM isn't one I can delve into here, but ebook piracy is a growing phenomenon. It's unlikely to materially impact your self-published work; but if you're paranoid, it is something to consider. The catch: Once you make a decision about DRM on most publishing platforms, you can't change your mind. It's on or off for life.
Always be promoting: Once you've submitted your manuscript to the ebook sellers, the tough work begins. You'll need to promote your book ruthlessly--which is what Facebook, Twitter, and Pinterest are for, right? Reviews are immeasurably helpful, but those can take time to get, and most reviewers prefer reading paperback manuscripts over ebooks. They are well worth the effort, though, as review blurbs look great on your ebook listing pages.
Make revisions: Luckily, you can change an ebook at any time. Whether you're fixing typos or adding new material, you can upload content in a matter of minutes. Upload freely and frequently.
Now that you know what you need, let's move on to the specifics each ebook publisher requires, starting with the biggest name.