Ned Marcus
Maester
It's not just about selling your book, it's about selling yourself as an author. You have a series of books? Put them all up! Write about why you wrote the book, what inspired you. Talk about yourself so that a reader who read one book feels more connected and willing to try another, maybe from a different series...
The notion that you have to write every day or twice a week or whatever to call it a "blog" is nonsensical. Write however often you feel like adding content...
In my experience, it was easier to add content and build a regular readership for non-fiction than it has been for fantasy. People were already looking for the non-fiction materials that I posted mini-articles on. That made it a lot easier to be "discovered", and to leverage the blog or website to promote sales. For fantasy, the blog or website is really more of a landing site right now: a way to connect with readers and hopefully encourage them to buy subsequent books.
I think the selling yourself part is important, and something I'm trying to do, but it takes time to learn how to do it. I agree with the second point, too, but I think it's useful to be regular, as I mentioned before. Certainly agree with your point about nonfiction. I also write nonfiction (and have a separate website for it) and it's so much easier to think what to write, and much more SEOable (if that can be a word).
I'm not sure how I missed your post before (I must have been in a rush the day I posted), but some good points.