Determine where the ribbon will be sewn onto the shade. One idea is to place to strips of ribbon on either side of the shade. Or try adding three lengths of ribbon, one in the middle and two flanking the middle ribbon.
Pin the ribbon in place from the top to the bottom of the Roman shade. Be sure to avoid covering the tape section on the back, as it is the working part of the Roman shade.
Add each pin carefully, make sure not to wrinkle the ribbon, as it will not lay flat when you sew it.
Sew the ribbon to the Roman shade with a straight stitch, removing the pins as you go along. For thin ribbon, stitch through the middle; for thicker ribbon, stitch the edges. Stop sewing when you reach the first wooden dowel. The dowels run horizontally throughout the length of the shade. Tie off the thread and cut it.
Reposition the Roman shade and continue sewing until you reach the next wooden dowel. Repeat until you reach the end.
Tuck the edge of the ribbon between the outer edge of the ribbon and the Roman shade. Glue in place.
Repeat the process for each ribbon you add to the shade.