Worked from left to right, the Herringbone stitch is a versatile stitch used for a border or as a filling stitch (filling an area within border lines). Varying the texture of the thread can make this stitch heavier or lighter in appearance. Patterns can emerge by varying the position of each row of stitches. The individual stitches can also be made further apart or closer together. When worked correctly, the pattern on the back of the fabric appears as two parallel rows of running stitch.
Check out this tutorial on the Cutesy Craft Channel: