A wonderful site and blog to check out: DaniDraws.com. Children's illustrator Dani Jones has posted a ton of fantastic tutorials, tips and much more for illustrators on her site. See her category links near the bottom of her main page.
Dani also recently launched THE ILLUSTRATED SECTION, an online store selling digital work (comics, picture books, art books, instructional, more) by illustrators. If you're interested in selling your work here, please read the submission guidelines.
Kidlitart recently interviewed Dani in a Twitter chat; see the transcript here.