There are many ways to do that, but interestingly enough, John Locke, one of the big early winners from digital publishing on Amazon, suggests not promoting your book heavily on twitter, at least not directly.

I'm going to write a post on the book soon, as I thought it quite interesting in its own right, and of course it's very relevant to LiberWriter. It's worth a read if you're at all interested in books: http://t.co/L9XOQ6U