I came across this video by Andrea Heckler called "Unusual Writing Tips."
Tip #2 Find Real Faces for your Characters seems particularly helpful. She uses photos of people to help her describe them.
I've not put it into practice yet, but I'll give it a try soon. Describing people is one of the things I need to work on. This may help. Thanks Andrea. Her webpage is http://realityinmymind.tumblr.com