When I draw portraits I intentionally start with an exaggerated sketch of the model. Exaggerated to the point where I can continue the path and make it a caricature or naturally swing to a straight portrait. I say naturally because I find that if I don't exaggerate in the beginning, that is figuring out which parts of the face really stick out, the portrait will be dull. Sure you might recognize the person but it won't feel like him\her. Drawing is a series of self correction and constant examination. I could draw pictures that "looked" like they people they were suppose to look like by age 10, but it wasn't till many years later that I felt they could be called portraits. This is not to say I am now a master portraiture artist, I still struggle mightily. I find that if I just tried to copy what I see exactly, the final product would suffer. This is why I like pushing the features and engaging the model (if working from life).