Pick up the piece of crown molding that is going to be installed and hold it horizontally in either hand. The molding should be about 3 1/2 inches wide. Locate the thicker side of the molding. Feel the top and bottom to determine which side is thicker.
Position a ladder where the crown will be installed. Climb up the ladder and place the molding in the first corner of the room. Put the thicker side against the top of the wall and the thinner side on the ceiling.
Hold it in place and look at the crown as it lies. Verify that the side against the wall has two grooves running across the bottom of the crown and the side against the ceiling only has one smaller line running across the crown.