The hard part is not the putting together, there are so many variations. The HARD part is thinking through the illustrations, creating a storyboard and actually getting all the sketches done.
So, assuming all that is done and you have the requisite 32 pages with front and back cover, you need your pages and your tools and a space to work.

( Note: in some cases the publisher will allow more than 32 pages.) In additon to this page there are two posts on my blog that give further information.

One uses a sketchbook with blank pages . and one is a simple way to create a dummy with out any stitching .

When I put a dummy together for a publisher or editor, I use only printed reproductions of the artwork. Once I have the sketches and several finished paintings printed out I use an adhesive glue dispenser to join the back edge of each page to the next.

When all the pages and the cover are glued at the spine side in this way, I enclose the entire spine with Art Tape to hold the booklet together.

When all the pages and the cover are glued at the spine side in this way, I enclose the entire spine with Art Tape to hold the booklet together.

By using matte brochure paper I can print on both sides with no bleed through. This makes a lighter package for mailing.
A 32 page picture book dummy will consist of two signatures, or sections of 16 pages each. In the dummy that translates to two sets of eight sheets of paper printed on both sides and joined to each other.

These are the tools... simple. A ruler... just in case I need to measure something.
Artist’s tape. Tombow adhesive applicator, and a white out applicator in case I see an error in the text or need to cover something I don’t want showing.
I never use staples. I know it would be so much easier, but they are sharp, can rust over time, and even if you tape over the binding of staples, they can sometimes tear through.

If I am asked to make a dummy book for a project I am working on, I like to make one for myself as well. That way if the publisher wants to make changes I can mark my dummy to match the editorial changes.

Your publisher will want your double spaced, typed manuscript along with the dummy as well as copies of one or two finished pages.

These are finished dummies . There are two kinds that I will do. Either the stitched up kind, or the taped kind.
Taping is much easier, but the stitched version has a wonderful book like quality and I like to keep at least one of those for myself.

I drew a little line over here ....................................>
to show where the tape is applied over either the stitched up version or the taped up version.

In the example below I have used artist's tape to attach the pages to one another after using Tombow adhesive to secure them in the initial stage.

Each page has already been printed separately and then adhered back to back with the corresponding facing side. That means I “glue” page one to page two to form one page. The tombow adhesive applicator is what I use . I run the “glue” around all four sides of page one and attach it back to back to page two. I do the same with pages 3-4 and then tape those two units along the spine with the artist’s tape.
I start by taping each page to the next and keep on going until I have the first 16 taped together along the spine.