|You can very easily keep your ruffles from wiggling around when you are sewing them down to your fabric, as I did when I was sewing my daughter's birthday dress.
I gathered my tulle in the normal way (using threads 1/8" apart) and pinned it into place on the underskirt. I then pinned over the top of the ruffles with long strips of tracing paper, which allowed the sewing machine foot to have a smoother surface on which to sew (rather than the bumps of the ruffles). When done, I simply cut/tore away the paper.
For a more detailed description, follow the link to my sewing blog: