I am a self made woman in drawing and painting. I never went to a course to learn it. But I've got it in my hands. And I think that the base to learn is the more you try, better it will be to make a drawing that look like the original. You have to find the good proportion of the model and make the volume of it, puting on it the lightness and the darkness: like if you see things threw a black and white camera. To succeed you have to try and try again.
I am not a good writer never in english, I hope you would understand me.
Once I talk to a professional painter and he gave me some advices and encouragements.