I took 2 kingsize vintage pillowcases ( thrifted for $1/each), and one long sleeve crewneck striped shirt from Old Navy Clearance ($1.97).
So I cut the two pillowcases up the seam sides, turning them into two flat pieces of fabric. Using the edge that was already hemmed as the bottom of the skirt, I cut it down to the length I wanted. Then I serged the raw edges so they wouldn't fray. I put both pieces together with right sides facing and seamed up the two shorter sides. Then I used my longest straight stitch to baste the top edge for gathering. make sure to back stitch on one end, and use the other end's bobbin thread to pull the stitches into ruffling fabric. Sorry I didn't get a picture of this.
After that seam, You are done. Seriously.
The instructions for the dress at Elle Apparel are probably better. However, she used all stretch fabrics, and I used broadcloth pillowcases and that's where the elastic comes in. I covered the elastic with my cool thrifted belt.