I think you're off to a good start, too!
Not that I'm a drawing pro, but the best advice anyone ever gave me about drawing was "draw what you see." Sounds simple enough, I know, but what it means is that you have to really look, really observe what you are look at, and draw exactly what you see.
Faces are really tough to draw. What helped me a lot with proportions was a grid. If you can get your hands on a transparency or other clear sheet of plastic, and draw a grid on it, then lay it over the photograph. Then lightly draw a grid on your piece of paper. Then when you draw you have the two grids to reference, and you can match up what you're drawing with the photograph (does that make sense?) That really helped me to learn.
And I think the most important thing is to practice, practice, practice.
Great job, keep it up!