Remember you can click on the photo for a larger view if you need it.
I'm using Catelynne, 9" paper from TAC's Fly with it collection. You will want to score on the back side of your paper in the center. So, for 6" paper score at 3", for 9" score at 4 1/2", for 12" score at 6 and so forth and so on...you get the idea! Now flip your paper 90 degrees and score in the center again.
Flip your paper over & cut from the front so you can see which way your decorative paper will go. You'll notice the paper has 4 quadrants now. Upper left, Upper right, lower left, and lower right. Your upper quadrants will be the pages in your book. The lower quadrants will be cut down and will become the base of the book when it is opened.
Cut between your lower sections right in the center from the middle to the bottom. After your cut, turn your paper 90 degrees to the right. That will put the right edge on the bottom for the next step.
Remember you will have four sections for your book (or 8 pages). The back side of page 1 will be your front cover, and the back side of page 8 will the the back cover. You can incorporate a space for a ribbon closure or a clip to hold or tie your book closed or open, but I would wait to adhere ribbon until all the pages of the book are adhered together.
If you are NOT using double-sided paper, you will probably want to ink the folds that will become your books binding.
Photos of the book open & closed: