One of my favorite things is to work on illustrations that have the same characters and scenery as a story I'm working on, but that has nothing to do with the story itself. The challenge I give myself is to tell a story in one picture using no words. There is such an intimate collaboration between text and illustrations in picture books that it helps to reinforce that even if there were no words, the story should still be understandable, relatable, and impactful.
So I started with the premise of Millie giving out free dolls in the likenesses of her friends, which they eagerly accept. But then it turns out she is only really interested in learning more about voodoo. I didn't dive deeper than that. Does the voodoo work? Do her friends feel pinches or fall down if Millie drops their doll? Do her friends decide to make a Millie doll of their own?
Who knows? That's not the point. The point is that my art inevitably gets better, my story-telling abilities get more well-rounded, and I've told a funny anecdote that helps fill out the personalities of my characters.
I'm not sure if I will ever write a full-length story based on the idea voodoo, but it's fun to play with for a while!