Measure the width of the window. Cut a piece of tulle that is twice as long as the width of the window and is 12 inches wide.
Screw a 2-inch cup hook into the top right corner of the window frame. Repeat this with the left side of the window frame. If you have metal window frames and can't screw into them, use self-adhesive wall hooks.
Gather one end of the strip of tulle in one hand. Drape this end over the left hook. Drape the far right end of the tulle from the right hook.
Adjust the tulle so it droops neatly between the two hooks with equal or unequal vertical bits of tulle hanging from either side.