I just bought Simply Sashiko, Classic Japanese Embroidery Made Easy by Nihon Vogue. ISBN 978-4-8053-1624-5. It has instructions for the stitching order.
https://www.amazon.com/Simply-Sashiko-Japanese-Embroidery-Templates/dp/4805316241/ref=sr_1_1?crid=12D6SS0OWCTL4&keywords=simply+sashiko+classic+japanese+embroidery+made+easy&qid=1652652078&sprefix=simply+sashiko+classic+japanese+embroi...