The problem I had with doing the serpentine/wavy line with my walking foot was trying to use that metal guide you attach to the walking foot for evenly space quilting lines. I was surprised that my machine was moving the quilt left to right and it was hard to keep it on course.
found the best way was to use the white plastic thing that makes creases in the quilt top - I like it better than putting marks on the quilt. Then I just tried to aim the line through the center of the foot. I imagine seams would also make a good quilting guide for this stitch. I have a Babylock.