Practice practice! You'll get better. A few things about the human head: The eyes are about halfway down the head. The eyes are about 1 eye's length apart. The The nose is about 1 eye length and nose's nostrils match up with the eye's tear-ducts. The corners of the mouth match up to the eye's tear-ducts. The ears start a little bit above the eyes and end at about the nose, maybe a little more.
I could probably do a tutorial.
If you haven't checked this guy out, you should http://www.youtube.com/playlist?list=PL0373FA2B3CD4C899 He's very good at human anatomy and has lots of tutorials. I'd also highly suggest getting a graphics tablet(preferably a Wacom). They have a few in the Bamboo line that are under $100.