This is how I generally work from a photograph
I've taken. I take the print to Kinko's and blow it
up and crop it if necessary. Then I have two prints
made. I make a grid on one, and have the other for
reference without any lines from gridding on it. It
is the top photo that I folded and made grid lines on.
You can see the folds in it if you click on this image
and see it larger.
When I am doing a portrait, I never worry about
likeness in the sketch stage. Just general proportions
of the face. I then work it out on the painting surface.
This sketch is on newsprint. I will transfer it by putting
charcoal on the back of the drawing and then going over
the drawing while it is taped to the panel I'm going to
paint on (or canvas).
This painting is going to be 18 x 24 and in oil on a panel.