First cut out the bookmark. I made a plain one and then I did another with my companies logo.
What I did is use tabs for the outline of the bookmark. but don't use tabs for the slot that the elastic goes through.
NOTE: I used 1/8" plywood from a craft store. Inventables has something similar.
I did alot of sanding to clean things up. I didnt finish mine. but, I might. If you finish, I would do at least one layer of clear acrylic over so that none of the stain will ruin your book.
Next, I took 1.5" waistband elastic to about the size I wanted and thread it through the slot in the bookmark and used my trusty sewing machine to make a loop that will then hold the book closed.
Very nice choice of book to show for an example. :)
Jeremy Richards