You definitely have the right idea. When you start drawing, you want to think as simple as possible. Just like with the pear exercise in the drawing basics course, you want to simplify the shapes into very basic forms and separate the areas of dark values from the areas of light values. As for the proportions, work those out in the initial layin before you start darkening your lines. It may just be a matter of diligent measuring until you develop your eye. Using guidelines like the center line and lines to place the eyes, mouth and nose can help. Once you have your basic forms and separation of light and dark, you can start rendering. Don't worry about making it look nice until you have a really solid foundation to work from.