A gesture drawing is about the tension and energy of the pose. It's not about getting a likeness of the model, it's about getting the attitude they're showing. When you're doing gestures of a good model, then any one of them could be the starting point for a story.
At least, that's the way I approach it. I'm not saying that there's a particularly right or wrong way to do it, just that this is how I do it, and it has worked out pretty well for me so far. See it, Feel it, Draw it. In that order - and that is the important bit.
P.S. Check out http://holmesinccomic.wordpress.com/2011/08/22/gesture-drawings/ for an update to this post.