Hey guys,
Zeph, you're right about this having been discussed at length in previous posts but the way that I've been taught and found most evident in reality is that if you draw a line through the ball to the target, at no point should your club ever go "outside" that line. It should move inside going back, touch through impact and move back inside on the way through. I tend to cross this line from the inside to outside at impact typically producing what you would term a "natural" draw, with divots which angle right of my target and foot lines but a clubface square to these. My goal of course is to have each of these square to square at all times and just adjust my target and foot lines right or left depending on the shape desired. It seems to me the best ball strikers don't have a lot of movement one way or the other as far as shape goes...Sean O'Hair comes to mind...his shots just sort of "fall" one way or the other. I know this has to do quite a bit with equipment these days but this has been the case in my observation.
Again, there is another thread that debates this in detail with article references, physics lectures, etc. but for my purposes and having played, studied and taken lessons for 30 years this works the best for me. I will tell you that $2.00 alignment sticks, or whatever folks want to call them (they're really just driveway markers), are the best investment from a practice aid perspective I've made for golf as there are numerous drills for this very topic that they can be used for.