While I've heard all the same things and think this is all useful conversation, I'd also caution that following this list of guidelines would lead us to a world where picture books are pretty similar. I wrote a picture book a few years back that I loved, but I knew it broke every rule in the book. It was short, yes, but it was also quiet without a distinct Fancy-Nancy type character, and with no conflict or problem. I sent it to my agent (whose favorite saying is "There is always a market for awesome.") She sold it, and OVER AND UNDER THE SNOW has not only won more awards than any of my other books but also sells the most copies, hands-down. And it's not alone - think WATER SINGS BLUE, or BLACKOUT or ME, JANE - none of these follow the list of rules, but they are lovely and they do what they do perfectly. And that is perhaps, the most important thing of all when it comes to picture books, I think. Your book doesn't have to do what all the other successful picture books do - but it does have to do what it does so beautifully that it's impossible not to imagine it as a real book on shelves.