I'm doing two quilts like this right now for my ggds. I found that if I used a washable blue marking pen (from the quilt store---not my dd's marker box) and made a dot 1/4" from the edge where I need to stop it works wonders. I sew the square in, stop on the dot, take two back stitches, then clip the threads. Then I line up the dot on that diamond with the one on the next diamond, line the unsewn edge of the square onto the edge of the diamond then sew it. Then I do the last seam. I don't usually back stitch when quilting but these seams get tugged more than usual when I'm lining them up so I do it. I had a horrible time with the first couple of blocks until I started using the dot method. Also, do you have a vintage machine? If so, use it. They start and stop much truer than a lot of today's machines. With my new machines the feed dogs start to move the fabric the second I start pressing on the pedal. With my vintage Singer the feed dogs don't move until after the first stitch is taken. Hope this helps. You'll probably get a different answer from each person that types one. I can't wait to read them to see if someone else has a better idea than what I'm using. This is the first time I've done them.