In the world of picture books, you have to make every word count. Author Ann Whitford Paul's book Writing Picture Books encourages picture book authors to go through their manuscript and identify critical elements. Mark up your manuscript by underlining the first mention of the main character, the main character's desire, the time, the place, the tone, and the "wow" moment. Ideally, these elements are placed as early on in the story as possible.
For further reference:
Writing Picture Books by Ann Whitford Paul