Proper proportions is definitely step one, simple but important. Arms and legs are the toughest parts of the body to draw/sculpt in my opinion. The last link carl posted is super awesome for finding the simple shapes in arms/legs. A few things that help me with arms/legs: Know the bones and how they articulate. [url]http://www.bartleby.com/107/[/url] is greys anatomy online. Its pretty technical but a great way to see the names and shapes of the bones, where they articulate with one another, and even has the places where the muscles attach. For the forearm, being able to follow the Ulna is very helpful. Its easy for me to get lost in the mass beneath the elbow, so I always keep track of the Ulna, and it helps me find the rest of the planes and shapes I also try to start with a simple shape for the forearm, something like a box going into an ellipsoid. Then its just a matter of finding the details. The upper arm is more simple since there's only one bone, so I focus on finding the right places for the major muscles: deltoid, biceps, triceps and the ridge muscles which flow down into the forearm. Legs are tricky too, mostly in finding the correct curves. The best advice I could give would be to learn the knee. Don't make it too small or too large (I tend towards the former). Also, make sure the ankle looks correct. Oftentimes, the ankle can throw the rest of the leg off. When learning this stuff, I think of it in 3 parts which all meet; Proportions, major shapes/forms (describing large muscles or muscle groups given shape by bones), and minor planes (like smaller muscles and bony processes).

I already have a torso and head drawn but I don't know how to upload it here.