Shorten curtains that are too long and not hanging properly. If you are certain the curtains will not be moved to another window, shortening them is the best approach. This means removing the excess fabric, so the curtains will not be usable on a longer window. Because rod placement varies from window to window, you will get the best fit by hanging the curtains over the window, on the rod you will be using when the project is finished, and marking the spot on the fabric where you want to hem to fall.
Measure the curtains with the yardstick, from the top edge to the desired hemline, and add 2 inches.
Cut the excess fabric off, using the scissors and following the chalk line.
Place a straight pin every 6 inches to hold the folded fabric in place, and sew 1/8 inch from the folded edge, using a sewing machine set to a medium-length straight stitch. It will look as if you are top-stitching the folded hemline when you are looking at the back side of the curtain panels.