Lay the book in the center of a sheet of paper. An 11-inch-by-17-inch sheet should be fine for the majority of books, but the size of the paper can be adjusted.
Trace around the edge of the book and mark where the spine is located.
Make trapezoid flaps above and below each cover of the book and extend to the left and right of the covers to make the insert flaps. The insert flaps are between 1/2 and 3/4 of the size of the actual cover. If the book is a hardback also make smaller flaps to be tucked inside the spine.
Cut out and attach to the book. First tuck in the flaps into the spine, then bring the trapezoid flaps down before folding in the insert flaps.
Make another template cover out of polyester film and attach to the paper dust jacket using sticky tape. The polyester film adds an extra protective layer.
Photocopy the template onto your computer and the front and back covers of the book as well, using a printer with a scanner attached to your computer.
Copy and paste the book cover design onto the dust jacket template and print off to create a dust jacket with the original cover.
Import the template into a word processing document and type out the name of the book and any other pertinent information before printing out, so the identity of the book is always known.