From what I hear, it is common for people who are learning to draw to make lines and shading and whatnot too dark, losing the subtleties of the full spectrum of tone possible with graphite. In my case, I've always been pulled toward the opposite extreme. I tend to start very light, and finish very light, perhaps hoping that at some point I will return to a particular piece and add more detail, and actually fill in the areas that beg to be darker with darker shades. That's typically at least, sometimes I just grab one of those soft almost oily high numbered B pencils and try to channel my more negative sensations onto the page. Usually it turns into a godawful mess. But I guess it might just seem that way to me cause I had to put up with drawing it and living it.