This would be my 2nd 30 min. drawing.  In this drawing I believe there was more attention to the models muscles.  Here I wasn't able to get a structure of the spine because her back was facing me.  But understanding that torso in relationship to the shoulders was key in finding the foreshortening. Also i paid attention to dark and light lines to give the model a understanding of distance and lighting.  By the lower back you can see the darker line I made.  Also by the inner thighs I made my marks darker.  I trying to keep you lines light as i could so that the darker lines but appear richer.