Writing Spirit is written by Julie Isaac, who is a creativity coach as well as author. If you're the sort of person who likes to think about goal setting and creativity, then this is a good blog for you. It's packed with interesting little snippets, but very down to earth advice. She also hosts a live twitter chat every Sunday to discuss writing and creativity. Imagine hanging out with 2 - 300 writers! That would be a very busy chat indeed.
For more information on ways to use Twitter to leverage yourself and your sales, check out her category "Twitter". I've read a few blogs that talk about publicizing, but this article is very focused on how to use Twitter to be seen as an expert. She also talks about book promotions, and is the founder of WritingSpirit Community.
I don't think this is stuff is complex, but it is interesting, and may be useful.