Here is some work I did yesterday. I started with the reference photo open in photoshop. Then I drew in the skeleton on a layer above the reference photo. Like so:
Then I made the background image invisible but left the skeleton. I then fleshed out the form around the skeleton. I would periodically bring the background image up to see if I was accurate. This helped to show me where I was having issues. I had very few issues with the upper body and was surprised at how close I was. The only trouble area was the left breast, which for some reason confounded me. But, the legs and feet were where most of my issues occurred. I had to redraw them several times to get them right.
Here's the resulting work: