I am currently learning to sculpt the human face and have been experimenting with methods to get the proportions right, as I was struggeling quite a lot with it. I took a look at various drawing methods and came accross this "box method". The main point is, to make a cube with about 2/3 of the size of the sphere. Then divide it in half and copy one half and add it underneath. This divides the face into 3rths and gives you a pretty good idea where to place the eyes, mouth and nose. Using this method I could improve my sculpt quite a bit. Hope this is helpful for everybody who is struggeling with proportions too.