Measure the width of the wall where the crown molding will be installed with a measuring tape. Use the measuring tape and a pencil to mark the same measurement on the length of crown molding.
Lay the crown molding face down on the miter saw. The bottom of the molding should touch the fence of the miter saw and the top of the molding should rest on the miter saw table. Hold the molding in this position whenever you make a cut to the crown molding.
Set the miter saw to a 45-degree angle. Hold the crown molding firmly in place and cut the 45-degree miter.
Follow the same process, but with the miter saw set to a 22.5 degree angle, to make a 22.5-degree miter cut.