Editorial Anonymous is a children's book editor of some repute, with a wonderful blog which I look at often. It's well worth reading even if you don't write children's books.
A couple of weeks ago she wrote a fabulous blog post about how illustrated books are constructed, which you can read here. Don't assume that it's only going to be interesting to those of you who write illustrated books for children; it's going to be useful no matter what kind of books you write. Really. Go and read it now. But don't forget to come back here when you're done!