Composition and Rhythm
Most portrait artists like to have an idea of the layout of their painting before they start. The processes they use to get there may vary, but it helps to have some kind of a mental map, or composition, before they begin to paint. It always amazes me how rapidly people seem to start painting at my portrait group. If you have a sitter, take some time to wonder around looking at them and decide on a composition you like. Some artists use a view finder (a little rectangular frame) to peer through or alternatively you can use your thumbs and forefingers to make a box to look through.