First off, typically I will read through a script and underline or highlight everything I don't know how to draw off the top of my head. I then go and find some kind of visual reference or photo that will give me a better description. I talked about this some already when I posted about environments and researching.
For my figure work though, I have taken quite a few figure drawing classes. Then at S.C.A.D. (the Savannah College of Art and Design) I had a very intense figure construction class with professor Paul Hudson. This guy is simply a modern master, in every sense of the term. In his class we were given 3 foot medical skeletons and then proceeded to draw and then sculpt every muscle of the body onto the skeleton, then draw it again. We were tested on their medical names and placement. It was a very indepth study on the skeletal and muscular structure of the human body. I liked the class so much I took it twice when I had an available elective.
In general, I build up my figures using basic forms for the head, rib cage and pelvis. Those give me the landmarks to then place the limbs and musculature over it all proportionally. But it all starts with knowing whats underneath.
I avoid taking direct photographic reference because, while accurate, I feel it looses a bit of dynamics and life in the drawings. If I ever use reference for a figure its for a specific hand gesture, facial expression or dramatic lighting on a face. I get that reference by just doing it in the mirror and taking a picture of my reflection with my phone. I can then look at my phone for the specific lighting or pose that I need.