Here’s a really basic video on how to model a head. This just gives you an idea how it’s done.
If you liked that, here’s a more detailed video specific to Blender. It’s about 15 minutes long but would take longer if you were going to follow along because you’d need to pause it. It moves fast.
Interested? This guy from Blender Cookie is a master. Here’s a 10 part video tutorial. Enjoy!