To assure an ideal curtain placement, measure the depth of your window cornice to determine the perfect curtain rod size. Using a pencil and tape measure, mark the desired position for the curtain rods so that the rod is 4 to 6 inches above the window frame, making sure the curtains are only lightly touching the floor or float just above it. For good natural light, curtain rod brackets should be placed about 6 inches from the outside edge of the window frame.