The final touch in this case has been adding a bit of texture to simulate skin pores and to harden the image. I am not going to refine the portrait more than that as the point of the the tutorial was really about creating an effective grid on the picture we want to draw a portrait from.
With your grid in place you have a solid foundation to start drawing the portrait. I would start from the face and draw the shape of it as in the picture below.
If you want to practice drawing portraits of people, this tutorial from is invaluable – it tells you all about how to create texture, volume and style!