Experience and imagination IMO, like you have to have a mental image of what you are attempting to draw, and practice so you know how to get the shapes and heavyness that you want. I guess the really good artists get to a point where they don't think about individual lines and strokes etc, they just have to focus on the mental image, and it almost draws itself.
I actually think that translates to writing too. Too often I get stuck on individual lines and paragraphs and lose touch with the flow of the whole thing. Umm so yeah.