Measure the wall length and mark the molding
Identify the spring angle of the crown molding
Set the miter saw to the correct angle for the spring angle
Place the molding upside down and backwards on the saw
Position the top edge of the molding against the saw fence
Cut the first inside corner piece with the miter angle set for the left or right side
Cut the matching piece with the opposite miter angle
Dry-fit the two pieces together at the corner
Trim slightly if needed for a tight fit
Nail the pieces in place
Fill gaps with caulk or wood filler if necessary