Gather PVC piping that is bendable and malleable. You should be able to bend and shape the PVC piping into a hula hoop shape. In fact, hula hoops can also be used if you'd prefer not to take the time to bend and shape the PVC.
Take the hoop you have created and pull the skirt over the hoop, centering the hoop toward the bottom or in the place that best achieves your desired look.
Use a needle and heavy-duty thread (sturdy versions can be purchased at sewing stores, and you will need a wider-eyed needle to fit the thread) to fasten the hoop to the interior of the skirt in various places. For example, you can place a stitch, then cross over the hoop and place another stitch. Going back and forth in this manner will fasten the hoop in one area of the skirt. Space these "back and forth" stitches approximately every 4 to 6 inches.
Hold the skirt up to make sure that the hoop has been fastened underneath and is level. While wearing the skirt, wearing a crinoline skirt or petticoat under the hooped skirt can create the added fullness you may need to get the full hoop-skirt effect.