This tutorial is for people with a grounding in InDesign already. You should know the basics of creating a new document, adding Paragraph Styles and manipulating text. I'll be covering the "gotchas" I found creating an eBook from InDesign. Creating an eBook in InDesign will give you the option to export as EPUB, PDF and HTML all from the same source, with minimal changes. What follows is my preferred flow.
Regular readers might want to tune out now. Go read an old Rex Havoc or something.
Before you start you'll need Calibre. Calibre is a "swiss army knife" for eBooks. It converts to and from all sorts of formats. To keep the code as pure as possible though, I only use it for the final conversion from EPUB (eBook format) to MOBI (Kindle format), which is not currently possible straight from InDesign.