Put on the skirt and the heels you'll wear with the outfit. Enlist a helper to pull the back of the skirt out behind you, and step forward a few paces to encourage the fabric to fall naturally.
Instruct your assistant to stand facing your back, and have her grab the fabric 6 inches below the lower curve of your bottom. Her hands should be aligned with the middle of each cheek. Ask her to lift the pinched material up and pull both hands in to create a triangle of fabric just below your tailbone.
Have your helper stick a pin through the gathered fabric to prevent slipping as you remove the skirt. Invert the skirt and secure the bustle from the inside with a few heavy safety pins. Turn the skirt right side out and remove the pin on the outside of the skirt.