Take measurements of the wall with a measuring tape. Transfer the measurements to the crown molding.
Set up the miter saw and crown molding. Position the miter saw to a 45-degree angle. Lay the crown molding on the saw so it is upside down. The top edge of the crown molding should rest on the table and the bottom on the fence. Hold the crown molding firmly in this position.
Cut the first corner of the crown molding at a 45-degree angle. Reposition the saw to an opposite 45-degree angle, and cut the opposite side of the corner. The two pieces of the outside corner should then fit together perfectly.
Nail the ends of the molding in place with a pneumatic nail gun.