Measure the width of your window and multiply by 2.5. This is measurement "A."
Measure from the curtain rod to where you want the curtain to fall. This is measurement "B."
Cut a rectangle of chiffon that has measurement "A" as the width and measurement "B" as the height.
Fold the edge where the top of the curtain will be, making a fold that is 3 inches deep, and iron it flat. If the chiffon is made of synthetic fiber, protect it from the iron by laying a towel on top of the chiffon before ironing under the lowest heat.
Slide a strip of iron-on fusible interfacing into the fold.
Iron the fusible interfacing into the fold, creating a firm, finished edge.
Attach curtain clip rings to the finished edge, leaving between 3 and 4 inches between each ring.
Thread the curtain clip rings on to the curtain rod.