Pictures of the Original
Please note that I have no good image of the back of any of the costumes where Lucilla wears this sash. While this method works for me and gives the right image from the front, I cannot guarantee that it's movie accurate.
It takes about 8 yards of ribbon to make this work on me. I'm a larger woman, so you may need more or less depending on your body.
Start with the center of your sash under the bust. Bring the ribbon behind you and tie it.
Bring the ribbon underneath your armpits and over your shoulders and tie it again.
Cross the ribbon over your abdomen and bring it around behind you.
Cross it behind your back one more time.
Now bring it around across your hips and tie a big bow in the front, letting the ends dangle. The finished product: