With really crappy photos. I'll apologise in advance for my camera, which isn't great at taking closeups. Also, this is only part 1 since I've not gotten the cover put together yet.
Text block; signatures with precut holes for sewing
First signature: start on the outside and sew up through each hole, then back through the same hole leaving a loop
At the end of the first signature, go in through the first hole of signature #2
Coming out through the second hole in sig. 2, go through the loop in sig. 1 and pull string tight (but not so tight the loops start shrinking)
Pull gently on the next loop down to tighten the first loop on your thread
Sew back into the same hole over the top of the tightened loop, then up through the next loop to repeat the process
View from inside the signature
On the last loop, pull out remaining excess string, and when you sew out of the last hole of sig.2, tie the tail and your thread together before entering sig. 3
To attach remaining signatures, continue sewing up through your holes, wrapping around previous connections as shown before sewing back through the holes, which creates the bnraided effect across the signatures. Pull everything tight at every step along the way to keep your string from being saggy or bunched up.
The finished result! The pencil markings on the right side in this photo are a guide I used to help line up the signatures correctly. I tied off the end of my string by wrapping it around previous connections a few times and dapping glue on the knot. I'm planning to cover the ends of the spine with a partial leather spine, so the marks as well as the odd looking braid of the end holes will be covered. To make a better looking braid at the ends, you can simply wrap the needle back between the top two signatures in the opposite direction after you make your usual connective stitch between the 2nd and 3rd signatures down.
At this point, you can prep two cover boards with the cloth/paper of your choice, spead glue all over the back and front of the text block, and glue the covers on. I'll post pics of how I do covers at some later point.