In here you can see some of my current techniques when detailing a head; it's not the best example... overall I'm not very happy with the sculpting part on this one, but I actually really like the final image. I've made some radical choices along the run, particularly when I changed the head shape by making his jaw way smaller. I think it kinda worked, but then I completely ruined the mouth, making it even worse when creating those terrible wrinkles bellow it. As I said... not the best exemple, but, for the most part, that's how I do it.
Btw, Youtube always choses the worse possible image to use as "thumbnail". I read it is the exact middle frame of the video; I'll see if I can do anything about it, next time.