Thanks for the tip cumquat, I'll try that out today! I always seem to draw them too small at first, then overcompensate.
The way the sketchbooks work is fairly simple, you just mosey on over to that section and make a thread. Title it whatever you want (generally your name) and start posting. A lot of people like to put little introductions in their first post, but if you're like me and uh...attention-averse... you don't have too. You can upload images using either the attachment tool (which is kind of a pain) or just an img link. Commenting on other people's sb's will generally bring traffic to yours.
Your heads/faces are crazy good man, I've no tips to give.