Step 1 - Take your piece of fabric to your sewing machine. (I've got mine threaded with black thread so you can really see what I'm doing here.) Pull the thread from your need to the length of what you are getting ready to ruffle plus about 3-4".
Step 2 - Set your machine to sew a zig zag stitch, we'll talk specifics of the stitch in a bit, for now - lets just focus. Sewing machine, thread pulled out from needle laying over the fabric... new sew straight over that thread with your zig zag stitch all the way to the end.
Step 3 - With your finger on the end of the zig zag stitch, pull the thread that you just sewed over and watch your fabric ruffle up right before your eyes.
Now you can see above how my ruffle is tight in the middle and not so much at the right. That is because used a very long stitch on the left, and a very short stitch on the right. The longer the zig zag, the tighter you can get your ruffle.
There you go...
Attach to your project and cut your extra threads. I do find that attaching with a small zig zag stitch, short and narrow, helps the ruffle stay ruffled on your project.
So, like I said yesterday, I'm not sure this is the best way to ruffle, if you've got a better way, I'd love to hear it. Doing 20 ruffles plus this tutorial took me about half an hour... with the "help" of Bug.