I did this pencil sketch from a photo a while back and was very disappointed! I'm not so good with pencil sketch for portraiture. I think you either need to be incredible subtle, or go the other way with vigorous markmaking. It was a timed sketch aimed at speeding up, and I did it in front of the TV.
But, waste not want not. I used the sketch as a tracing onto canvas and started to fiddle around with an acrylic portrait. Obviously not finished, but thought I'd show the process of the first day.
My method of painting, is to go round and round the space adding refinements as I go, until magically it tells me it's finished. I don't complete the painting in one part and then move onto the next part, so bear with me!