Sculpting faces is very time consuming and something that I work on throughout the entire sculpting process. However, before I begin another area of the sculpture I like to get a good foundation for the face. I use to save the face for last only to discover that I ended throwing the entire sculpture off when the face was completed. The problem is that the face would end up too big or two small for my piece. I just recently started sculpting the face first and I think it has made a huge improvement in my overall work.
My goal is to knock out at least 80% of the face before I begin another area of the sculpture. I will continue to bounce back to the face during the sculpting process. Even though the majority of the work is done up front, I still end up finishing up the face around the end of the piece. However the foundation was already built so the only thing left at the end is perfecting (to the best of my ability) the little details.