I like to work on portraits for demonstrations... because there is something magical about watching a face slowly appear from a piece of paper. So I did this portrait of my friend Maggie's son Will. She said I captured his smile well - so I am really happy. Getting the expression right is very important to me when doing a portrait. Its not getting it to look like "a smile" or "a scowl" etc that is important... its about getting an expression that the sitter would make. If you give them a smile they just don't make - then to the person's friends and family it won't look like them. You won't have a good likeness.
To be able to get the expression right, I rely very heavily on not just the features but how those features connect. If the corners of the mouth are up a little, for instance, the cheeks will be raised, as well as the lower eye lids.
On another note - I picked up copy of James Gurney's new book "Imaginative Realism" recently. I am a big fan of Dinotopia and his amazing blog where he shares loads of painting/illustration information. When I saw a listing for his book in an art magazine - I wanted it because I thought it could be helpful for teaching my kids at school for when they want to draw imaginary things... but boy is it a great book. First of all - it is eye candy.... which is a must have for art books in my opinion. If there aren't loads of good artwork to see in it, I don't want it. Next he puts it to the reader plain and simple - you have no doubt after looking at it that you will have to work hard to make a realistic imaginary thing... not only use creativity. You will need to do research, use models and perhaps even make models for imaginary creatures, etc. There is also just plain old good advice for painters in there too about composition, lighting etc.
I found the pages on what he calls "the windmill principle" really interesting. Actually you can read it on his blog... http://gurneyjourney.blogspot.com/2008/04/windmill-principle.html
as well as flagging the head http://gurneyjourney.blogspot.com/2008/05/flagging-head.html