Not hanging a window treatment properly. Architects may disagree, but I (almost) always hang draperies and Roman shades from just below a molding or ceiling to elongate a room. Draperies should at least kiss the floor
Interesting idea to double layer. How to make double layered Roman blinds so you can leave the light shades down in the day to filter light, and the darker shades at night to block from the road/outer lights, etc.