Use a tape measure to determine the length of the crown molding needed.
Measure the crown molding and make a mark at the point to be cut.
Rotate the miter saw to the 45-degree position. To rotate the saw, pull the handle on the bottom of the saw toward you and then rotate the saw. When cutting crown molding for a tray ceiling, you will use inside cuts, but the molding is held upside down; so if cutting the portion of the molding to be placed on the right side of the ceiling, move the saw to the right and vice-versa.
Position the crown molding against the miter saw fence and table. When cutting the molding, rotate the molding so that it is upside down. With the molding upside down, place the shoulder of the molding against the saw table and the foot against the saw fence. The molding should be positioned as if the fence is the wall and the table is the ceiling.
Align the blade with the mark made on the molding.
Put on your safety glasses and squeeze the trigger on the miter saw, passing the blade through the molding. Be sure to hold the molding with your other hand, but ensure that your hand is far away from the saw blade.