I usually sketch a portrait of my subject "alla prima" (in one sitting).  The immediacy of this approach keeps the work fresh and unlaboured.  When I am commissioned to work on a portrait, or when I am painting a portrait for a major competition submission, then the process becomes more layered, working from live sittings and from my photographic references of the subject. The painting of a portrait is a rewarding experience, affording me the priviledge of getting to know my subject in a unique way.