I learned a new way of doing ruffles about five years ago, and it is so easy.
You need thin cotton yarn. Centre your string in a line where you want your ruffle to go. Use a wide zigzag. This pins the string in place without sewing it down. I try to stay close to the edge so when I sew my 5/8" seam the string isn't caught in it.
This is what you have.
Now you gather your ruffles along the string. I have found this to be faster and easier than a double row of stitching. I'm usually able to carefully pull the string out once the ruffles are sewed down and save it for another project.
Have you done this? What's your best sewing tip?