If you are receiving Susan Fletcher's email tutorials for this project you will have all this information (and a lot more besides) but here are her instructions for establishing the order of stitching a sashiko design.
When stitching a sashiko design we need to think about the order of stitching. By stitching in the right order we will not waste any precious thread, or waste time, and we will be able to get into a good rhythm and keep our stitches even.
This usually means identifying the continuous lines within a design and following those rather than stitching motifs individually. With this design the first thing to stitch is the line of curves from one side of the design to the other.
So I completed all the horizontal curved lines first:
If it is not possible to stitch in long lines then we need to make the jumps between stitches as short as possible. Generally speaking, if it takes less thread to cast off and cast on again at the next point then that is what we should do.
With the blowing grasses pattern the next stage in the order of stitching is the small grasses and we can see that they form a diagonal pattern of their own and this is the order in which we stitch.