I don't really know about books, but if you really want to excel at writing, I'd suggest you practice. Start a blog, or join a article submission website such as
Ezine Articles.
Books can teach you a lot, but I've really noticed my writing has seriously improved ever since I started practicing. And by practicing, I mean writing 2-3 400 word blog posts everyday. Gaining better writing skills wasn't really my goal when I started these blogs, but it's a nice bonus.
