RUNNING STITCH - From "The Gentle Art of Stitching" by Jane Brocket. Here are illustrated examples of Kantha, a traditional form of handwork in rural India and Bangladesh encompassing a wide range of design that uses only the running stitches.
Since then we have produced a number of project specific tutorials which may be a more fun way to learn sashiko stitching. I recommend Dragonfly Over Diamond Waves and& Dragonfly Above the Earth . Learn the art of Sashiko, a Japanese Traditional Hand.