Here's a quick image from the back of the quilt of my double-stipple for the curious.
The pairs of lines are about 3/16in apart, to give an idea of scale. I simply sew a medium-scale stipple, then loop back 3/16in next to the original line. I do a bit at a time, and you can see here where I've branched-off to do the next section as well. As long as you're careful to loop back on the right side, it's pretty easy. Now, I'd better get back to it!