I have used this gathering technique from The Family Homestead almost exclusively since coming across it on the beloved Pinterest. It really does simplify the struggle that gathering ruffles can sometimes create. By providing a sturdy pull thread, the gathers come together quickly without breaking threads. Love it! (breaking threads makes for a very cranky mama!)
Here's an example of how I've used this technique recently.
I use yarn instead of the crochet thread like the original tutorial suggests. I have yarn on hand, it's very inexpensive and I've found it slides out of the stitches easier if your zig zag accidentally catches it, where the cotton threads want to become part of your ruffle. :) So, line up your yarn in the center of your presser foot and sew the yarn to the top of the piece of fabric you wish to gather using a zig zag stitch.
Then you simply gather as normal. However, The Family Homestead link above has some great tips on gathering as you pin so the ruffle fits the piece it's being attached to as you go. GREAT IDEA! I'm always having to let my gathers in and out! :) You'll want to check it out! Don't you just love learning new techniques that make your sewing experience even more fun!?
Ok, now you are ready to sew the ruffle to the fabric it is pinned to. The yarn can serve as the perfect stitch guide as you sew too. Just line the edge of your pressure foot up with the yarn and sew.
Once the pieces are attached, you can then pull the yarn out. If it won't come out all at once, picking it in a few different spots throughout the stitching will do the trick. No worries if you pick the zig zag stitching either as it has already done it's job!
All that's left is to turn, top-stitch and then admire your finished ruffly gathered goodness!
I hope this helps others the way it has me!
Happy fluffy sewing fun!