I usually let the subject choose what facial expression they make, whether or not they want to pose, in what direction they look etc. This helps to give my photos variety, and the process becomes collaboration between me and the subject; I am portraying them in the way they chose to be portrayed. However, the in terms of quality, the results vary.
Most of the time, the best photos are taken when the subject doesn't seem to care that a photo is being taken. Sometimes though, I find a person who can look right at the lens and smile completely naturally.
You can see this photo in high quality along with many others on my Flickr page.
