Draw more from life and not from photos. A person's foot is as long as their forearm, but in the photo it's not evident due to foreshortening. But since you haven't picked up on that the foreshortening on the drawing is non-existent and she has tiny feet.
There are other factors that contribute to a photograph's 'flatness', which is why it's better for you to study from objects in front of you.
Get reference for the lighting as well.
Slothboy is entirely right. You need to feed lots of correct information into your visual "library" before correct information comes out.
Another thing that would help is copying somebody like Loomis or Bridgman. You don't have to make a career of it, just spend some time, a little time each day maybe, making the closest copies you can of their anatomy drawings. What they teach you is to find the body's forms -- pelvis, ribcage, skull -- and turn them convincingly in space. They teach you proportions and foreshortening. I found Bridgman especially good for visualization, but everybody finds a favorite artist to copy.
It's not bad, honestly. You just need more of the basics.
I was once on the receiving end of a critique so savagely nasty, I marched straight out of class to the office and changed my major (sketchbook).
I understand that drawing from life is a HUGE one. I myself advocate this. I have a situation where I don't get many chances to draw from life.. but maybe I am looking at it wrong so help me out. Where do you go when you want to draw from life? I carry my sketch pad everywhere. If I have to wait I try to sketch the people around me. This doesn't happen often and its in short spurts when it does happen. If I am not getting many changes to draw from life what else can I do (Not avoid drawing from life, but trying to maximize time spent learning. I have Loomis's book "Figure drawing for all it's worth" and I have read it.
Get a big mirror! As for drawing from life, depends on where you usually go... I don't know - libraries, coffee shops, malls, cafeterias, crowded parks, sporting events, grandma's house. Whatever is around where you live. I sketch while my daughter has swimming lessons. Bored parents make good and fairly stationary subjects.
Also, depending on where you live, look for open figure drawing. The local community college and several other places close to where l live have open sessions where you just pay a few dollars for 3 hours of figure drawing. You just show up and draw.