Serging is a good way to finish raw edges, since the stitches are formed over a newly trimmed edge to give a neat finish. A purpose-made machine is needed.
Adapted from "How to Use, Adapt, and Design Sewing Patterns," by Lee Hollahan and published by Barron's Educational Series. Lead image from flickr.com/kellyhogaboom.
Make a seam with right sides together and sew a line of stitches 5⁄8in (1.5 cm) from the edge.
Thread the serger with three threads and skim each of the raw edges of the seam to finish.
Iron lightly over the right side to press.