"Picture books are a marriage of two totally different story telling styles. The writer tells a story in words, and then the illustrator tells the story in pictures. And the two story styles together bring something deeper and richer than either could alone. Even though the author and illustrator don't interact, the story is truly something created by both. You might begin your study in the public library, a school library, or a bookstore, but there are certain things for which you should watch:
STEP ONE: Check the copyright date. Be sure the books haven't been out more than two years (some say 10 years max is still okay). You want to come as close to what publishers are buying now as possible. What works in a picture book has changed over the years. This is very much an evolving form. If you're counting on picture books from your childhood or "classic" picture books being republished today, you're going to miss some important things you need to notice that will apply to YOUR book. Because YOUR book is competing with those other new books coming out now.
STEP TWO: Avoid books written and illustrated by the same person. A top illustrator can get a picture book published by one of the big companies even if the book is both very wordy and very much too adult. Also, since the illustrator controls the illustrations completely, the author illustrated book is a totally different creature from the book YOU are writing and selling.
STEP THREE: The same rule applies to celebrities - any kind of celebrity which included picture books written by writers for adults. Celebrities sell books based on their name, not on the content of the book. The book might be good, but it doesn't have to be - so steer clear of the celebrity picture book.
STEP FOUR: Nonfiction picture books are often quite a bit wordier than fiction. And nonfiction picture books by some trade publishers include a lot of fictional stuff but the whole purpose is to dump facts, so they follow nonfiction rules. Again unless you're writing a nonfiction picture book, you want to look at the books that represent the same sort of thing YOU are writing and selling.
After you've read 100 books, pick out the top five or ten that really "clicked" for you. The ones you loved the most. Then go and type out the text. Type it like a normal book manuscript, then put it aside for a few days or weeks. Now when you read it, you're reading what the editor read when he or she decided to buy the book. Notice how the action works. Notice the characters - what made them unique. Make a list of reasons why an editor might have picked THAT book out of all the other manuscripts he or she read that day. Do this with several of your picture book study samples. Now look at your book. Pretend you're an editor. Look at how YOU used action. Look at how you presented your character. Make a list of reasons why an editor might pick your book out of all that he or she read that day (that list may come in handy at query writing time). Be critical. What do the books that were published have that you didn't have? Go back and re-read your "study" books again. Now, without your ms open, begin rewriting it on your computer. See if it changes now that you've fueled your mind with publication-ready mss. Now compare the rewritten ms to the original. How is it better? How is it not as good? Work on a revision that combines the best of both."
And here's another article about mining stories for success. Very excellent!