I start by sewing a textblock on a sufficient number of tapes -- this book is only 6" tall, so I only used two tapes.
I cut two holes in the cover and pull the tapes through. I try to make the holes on the small side for a snug fit.
Then I fray the tapes out ...
... combing them with this tiny brush for eyelashes can be helpful.
I glue them down, and then put an extended muslin patch lining on the spine. The lining goes over onto the boards and is glued on top of them. For a sketchbook that lays open when flat, this is usually the only spine lining a book of ten sections needs. If you wanted better throw up, you could also put on a paper lining. Then I PVA the sides of the boards, to keep them from splitting, and cover the spine and corners with book cloth.
Sometimes I put a little matching "headband" on.
I also usually cover the inside of the joint with another piece of cloth, just for aesthetics. Plus, I think the frayed cords would be more vulnerable without it.
This is a sketchbook structure that has performed well for me. The laced in tapes provide a super sturdy board connection, but the process doesn't have so many steps that it's an obstacle to making more sketchbooks when I need them.