This article is full of great advice on how to write a book, whether you publish for yourself or for someone else.

I have written 10 books. 9 for the Pragmatic Bookshelf. I've made a nice side income on my books by doing many of the same things he lists. This isn't so much about self-publishing as it is about writing great technical content.

Full disclosure - in addition to writing, I am a development editor for the Pragmatic Bookshelf. But I publish my own books with them because they offer the best of both worlds. They split the profits with you 50/50, but you get an editor to work with throughout the process, and they take care of a lot of other things, like distribution, sales, billing, copy-edit, typesetting, etc so you don't have to.

But the important thing is to get your message out there to people in a quality way, like this article suggests. Do the research, find your voice, write about something people care about. If you go the self-published route, get technical reviewers, hire a development editor, and get a copy editor. Your end results will go far.

[edited to clarify value add for publisher]