The width of the ruffle should be about 25 inches, give or take. You can play with it a little bit and figure out what you like best. For length, I made the one in the picture about 10 inches long, but I wish I had made it a little smaller. The exagerrated look was a little too exagerrated. I would probably make it about 6 inches long at the midpoint.
Finish the edges of the ruffle with a rolled hem or a serged rolled hem.
Take the ruffle and find the midpoint. Take two large tucks on each side, going in towards the middle, adjusting as you like. You want the total width of the ruffle, once folded to measure 10-12 inches. Baste about a 1/2 to 1 inch down from the top of the ruffle, keeping your tucks in place. Attach to the dress just below the casing stitch.
Finish as directed in the pattern.
Ready for a night on the town!