Analyzing the structure of the manuscript is, for me, one of the first and most important steps I take in illustrating a picture book. This is not a complicated process. I identify what is the opening section of the manuscript: the part that "sets the scene." I pinpoint where the actual story begins: when do things "start happening"? Next: where are the final crisis and resolution? Everything following that is the "wind-down."
The second part of my analysis is to distribute the text amongst the pages of a dummy, or mock-up, of the book. At this early point my dummy is ultra simple: 8 pieces of 8 1/2 x 11 paper, folded in half and numbered. I mark in the possible positions for front and back matter. There will then be something like 12 double-page spreads available for the manuscript.
Out of 12 spreads, only 1, or possibly 2, of these can be used for "setting the scene." The actual story must begin on spread 2 or 3. Otherwise the reader will already be losing interest, wondering when something is ever going to "happen." Likewise, at the other end of the book, the final crisis must happen on spread 10, the final resolution on spread 11, with the final spread 12 for the "wind-down." After all, once the actual story is over, no one likes to hang around for a drawn-out good-bye.
The remainder of the text can then be divided up amongst spreads 4 or 5 through spread 9. This gives 6 or 7 spreads total for the main body of the story. If a picture book manuscript has a slow beginning, a weak middle, or a tedious ending, such flaws will become glaringly obvious as one divides it up into a dummy. This is why authors as well as illustrators benefit from putting a manuscript into a simple dummy like this.