Usually I focus on the face and on the eyes, but I'm never happy with it. Instead of starting by the eye, and doing it over and over again and never finishing a drawing, I do all the rest, the background, the body and do the face and the eyes at the total end.
I usually use felt tip pens, with no eraser, no control+Z so if there is a mistake, or the eye is not looking in the right direction, I accept it, there is no going back and, at least, the drawing is finished.