So after you've invented your story, and drawn out a storyboard for the 32 pages, you make it into mock-up book, a dummy book.
Everybody loves to see a dummy book. Friends, editors, designers, grandmas, neighbours... It's the first time you can show the book to someone and they start to understand what the story is, and you can judge their reactions on the turning of each page. It's also the first time you've put it all together, and it's a stage I really love. If I'm really excited about the book (which I always have been) I make a few dummy books along the way. I love to keep them and look back on them, and it's not usually until it's in this format that you see the holes/gaps/ errors in the flow of the story.
Other illustrators have told me they make a dummy book to convince their editor to commission the book. I make them to convince myself firstly, and then hopefully to make my editor fall in love with the story. Above are two of the dummy books I made for Otto, the red one was the very first, and for the second I had found the title font for my cover, which gave Otto a strong identity from the start. At this stage I'll also be thinking about the media I will use, colour palette, maybe looking at other books for reference, and drawing some rough covers.
When I make a dummy book I will just draw straight into the pages, Then using my old typewriter I type then cut out the text, and stick it all together. I use my computer later on, but at this early stage the simpler the better.
Ps. A beautiful dummy book can be a piece of art in itself, Mini Grey is a real master, she makes perfect little mock-up books.