Making a circle skirt? Before you hem it, hang it up by the waist for a few days. You can do this on a regular hanger, a dressform, a hanger with clips, or anything else that will support it by the waist and let the rest of the fabric hang freely. Re-cut the bottom before sewing.
Because part of the circle will be on the grain and part on the bias, the fabric will stretch unevenly. Hanging it before sewing the hem will allow the fabric to stretch out, allowing for a more even hem length on the finished skirt.