Well, I've been looking over the various anatomy books and have even done a bit of sketching. Picked up quite a few tips regarding proportions and the set up of a male character.
I've never really properly studied the anatomy of the abdomen - rectus abdominus, obliquus abdominus and serratus anterior and how they all fit together with relations to the rib cage. So the study has been a really useful exercise.
In order to place the serratus muscles correctly, a line is drawn from the pit of the neck through the nipple to the base of the ribs.
The arm is going to be a tricky body part to model and getting the rigging right will be tricky.