Measure and mark the molding with a tape measure and pencil, respectively. Note which angle you will need to cut the crown molding, such as 45-degree right or left, or a straight 90-degree angle.
Place the molding into the miter box. Line up the mark on the molding made from Step 1 with the correct slot in the miter box. Slots are at left and right 45-degree angles and a 90-degree angle.
Slide the miter saw into the miter box slot as dictated by Step 2. Move the saw slowly to start the cut and finish with long strokes.
Smooth the cut when you finish with fine-grit sandpaper. Remove all burrs using the sandpaper.
Place one piece of molding against a wall. Butt the molding into the corner. Attach the molding to the wall by hammering nails into the wood.
Set the second piece of molding onto a flat surface, face down.
Use a scrap piece of molding to trace the molding design onto the back of the second molding piece.
Cut along the line using a coping saw, drawing it back and forth across the wood. Follow the design carefully to create an accurate cut. Wear safety glasses and gloves to prevent injury.
Dry-fit the molding against the wall. Take a mental note of any areas that need a minor trim; mark the crown molding with a pencil if you cannot remember what areas needs trimming.
Trim the molding according to your mental or written marks using the coping saw. Hold the molding with your hands against the wall again to dry fit the molding and ensure a tight fit.