I recommend keeping up to date on Christopher Hart's work on ChristopherHartBooks.com. Christopher Hart is a professional artist and author. As I believe I've mentioned before, you can follow him on deviantART and Facebook. He posts some funny, wacky multiple choice questions, and he talks about making it as a professional artist. I've read some of his how-to books and they're very helpful to me as an artist. His latest book is How to Get Published as a Manga Artist. I recommend checking that out as well. It can be very helpful not only to manga artists, but other artists as well.