Some painters like to start with the detail, working up these areas to the finished state before painting the background. Some like to get half or three-quarters of the way with the detail and then add the background.
This is not an approach to use if you're uncertain of your brush control and worried you're going to paint over something when you add the background. Having a background that goes around a subject, or not quite up to it, will ruin a painting.
Tina Jones, whose painting Faces of Karen Hill is shown here, adds the background when she's at about the halfway mark. After adding the background, she then made the colors of the skin and clothing darker and richer, refined the overall shapes, and finally added hair.
