We've reached the end of the full sized sketches phase. Now is the time to look at all your drawings and make sure the tiny details add up.
There is a good article about character consistency for comic artists here: http://www.helium.com/items/949706-drawing-your-comic-characters-with-consistency Many of the points the author discusses are also relevant for picture book illustration.
Find someplace to spread out all your art so you can see every spread all at the same time. I use the floor of my bedroom. Other artists use a huge cork board on a studio wall. No matter how strong an artist you are, this step CANNOT be skipped. Big things to check for are:
• Facial features - does you character look like the same character from page 1 to page 32?
• Proportions - is you character the same size throughout? How about compared to secondary characters?
• Clothing - if your character has a costume, are all the details in the same place?
• Environment - is your background and supporting imagery also consistent with character and story line? Has your setting undergone any changes? Should it have?
• This is also a good time to double check your page turn and story flow. Are the images working to move the story forward as you intended in your thumbnails?
There may be a spread (or even two) you decide isn't working and will want to revisit them. In one book I was working on, my main character's skirt and hair grew longer. Since the story time elapse was a single afternoon, this was not a natural occurrence and needed to be fixed before any color was added. Such details are not readily observed unless all the art is set side by side.
These are the full size pencils being approved at Puffin: http://thepuffinblog.typepad.com/.a/6a00e5501c1be888330115705ac655970c-pi