this was just a head practice in photoshop cos i felt like it. It was going to be a guy at first, then it started looking like a girl so i went with that. I thought i'd post the stages it wqent through to get there, just in case anyones interested.
Basically i rough in the features, then erase and smudge in the lines that i want to keep. then start getting the shading in with a soft airbrush. Pretty much the entire process is just the soft airbrush to paint with and the smudge tool used copiusly to smear lines and alter features until it starts coming together. The smudge tool is brilliant. I use it once i've got the features roughed in to shape and mould my character like a piece of clay, then just use the airbrush to paint in refinements. All done in black and white until i'm satisfied, then i add a 'colour' layer, finishing up usually just with a 'levels' adjustment layer to get the tones right again over the colour layer.
If you've got any more specific questions feel free to ask.

Photoshop cs2 with wacom tablet. copyright dypsomaniart 2007