Profiles and shoulder axis

I just used to 2 min practice tool for the first time and I have to say, it's pretty awesome. It is making me look at the subject much closer. I did however discover I have a problem that I didn't know I had. Whenever a picture came up of a profile of the subject, I was baffled as to how to lay down the axis of the shoulder girdle (from clavicle to clavicle). This for me is one of the first few points of reference I drop to line up he rest of the drawing, and im finding I'm not even coming close to a realistic depiction of where it should be and the torso then becomes oriented incorrectly. How do I deal with this problem? And advice would be great.