Its acctually also a question on what should I work on further (shading... figure shading.. ) Stuff like that...
With other words!!.. CRIT ME!
I would suggest pushing the values darker right now. It'd be sweet to see some darker darks in a couple places. Maybe think about adding a background too, doesn't have to be anything fancy, just something to ground them. The dress falling onto the ground helps to ground them, but a background/horizon would still be nice.
My two cents.
The piece appeared a little dirty (smudges in background areas look oily). Please read this page about handing charcoal and graphite.
You need to place emphasis on correct Chiaroscuro to clarify your shadowed areas. I agree, some form of background could also improve the composition.
A book that may assist you.
Dynamic Wrinkles and Drapery: Solutions for Drawing the Clothed Figure
By Burne Hogarth