Pimple?!? er... damn google translator... what is a pimple?
The grainy look was not intentional, it comes from using soft pastels (pencils,dunno the exact term in english, wood sticks with an inner stick of color) on paper: the grain is given by the softness of the pastel, the grain of paper - this was very smooth though-, and the speed at which you trace lines on it.
I think nobody is born with the ability of doing things, there are just people that discover a kind of natural ease in doing some things. As u said, I taught myself by tring, rubbing, redrawing one million times, until I was (almost) satisfied. It was very frustrating, but worth all the effort.
The fact you can shade realistically should make you happy! DO IT! Speed will come after trying many times!