Following are links for a couple of sites that - although for painters - do give excellent ideas on how to do protraits. Myself, I found the ideas quite interesting - and will be helpful - in laying out a portrait.
http://www.portraitartist.com/index.html
http://www.mastersofportraitart.com/portraitartists.htm
http://www.mastersofportraitart.com/calibrate.htm
The last one is a screen calibration from the protrait site to get the best from the reproductions.
Norm D