During the past year, I have had several breakthroughs with my picture book writing, and it's all thanks to doodling.
I used to just type up a story and assume that an editor and illustrator would be able to make it fit into 30-32 pages... but ever since Eugene's lecture at SCBWI, I've realized the importance of visual page-turnability. And so after I write the first draft of a book on the computer, I print it up and then pretend I'm an illustrator. I sketch the story onto my journal, and see if the story actually works on the page.
My new "Rainbow" themed book is my latest success story. The first draft was pretty good, but after I created a sketch version, the writing improved tenfold.