This is how I made a scalloped hem on my in-progress pencil skirt. The first half of the photos were taken at night - hence the crummy quality. The fabric is a celery green cotton sateen.
1. Find a circular object (glass, bowl, candlestick...) that is about the size you want your scllops. If you have a few of them, lay them in a line for an idea of scale.
2. Do a little math: Measure your hem all the way around, starting and ending at the back vent or back seam. Divide by the diameter of your circle to get approximately how many scallops you will have - I had 6 on the back and 6 on the front. You will probably have to fudge a bit.
3. Use an eraseable pen to trace your circles around the hem, making sure they match up at the center back.
5. Turn the scallops out. this is where it got tricky to make them smooth. I finally decided to try a template cut from cardboard that I slid in each scallop and ironed. It worked out great!
The scallop template for ironing.
All ready for a zipper and waistband!