Sashiko patterns are worked in continuous lines and knots are not used. Thread tails are typically not seen on either side of a traditionally-worked design. Instead, the tails produced by starting and ending a length of thread are hidden between the two layers of fabric. For designs that are not to be seen on both sides, a temporary away knot can be used, and thread tails threaded through the back side of the stitching.
The sashiko stitch is worked in the same manner as a basic running stitch. The only difference is that the space in between each stitch must be half the length of a full stitch - the stitches are longer and the gaps are half the size of the stitches.
Sashiko patterns should be worked in heavier embroidery threads such as all 6 strands of embroidery floss or a size 8 or 22 pearl cotton on on plainweave fabric with a slightly loose weave. The fabric should be heavier than broadcloth but lighter than denim.
The loose weave allows the needle to move in and out of the fabric with ease. Bottom-weight fabrics such as denim and twill are too heavy for sashiko, but cotton/linen blends are usually a perfect weight. You may need to experiment to find the right fabric.
Use a long needle with an oval-shaped eye that can easily accomodate the thread. Darning and milliners' needles are good choices for Sashiko.
When marking the sashiko patterns on the fabric, use a water soluble marking pen or a pencil for best results, as you do not want the marked lines to be permanent.