Some friends and I are studying Ann Whitford Paul's wonderful book Writing Picture Books.
I tried studying it on my own, but didn't stick with it. Hopefully with a group we can power through.
I'm hoping that after Writing Picture Books we can move on to other great books. Here's the list we've compiled:
Writing it Right - Sandy Asher
Writing Irresistible Kidlit - Mary Kole
Save the Cat - Blake Snyder
How to Write a Children's Book Vol. I: Structure - Eve Heidi Bine-Stock
How to Write a Children's Book Vol. II: Word, Sentence, Scene, Story
How to Write a Children's Book Vol. III: Figures of Speech
The Nuts and Bolts Guide to Writing Picture Books - Linda Ashman (Thank you Cathy Ballou Mealey!)