Here is a simple method for transferring a sashiko pattern onto a piece of fabric for easy stitching. Anywhere you can get a lovely line drawing is perfect for a sashiko pattern. Once you get your design, my suggestion would be to photocopy it and enlarge or reduce to the size that you want. (Always keep your original copy.)
Place your fabric on a hard surface. Don’t use a textured surface, I recommend using a cutting mat. Centre your pattern on the fabric, and place a sheet of tracing paper chalk-side-down between the fabric and the pattern.
Using a stylus or a ball-point pen, very firmly trace over the entire design pressing very firmly on the stitch length.
If stitch length isn’t indicated, then you should trace in your own stitch length.
Check that you have completely traced the entire design onto the fabric.
If you find the design is fading while being stitched, simply use a ceramic pencil to enhance the design markings.