Glen Keane (the legendary Disney animator) once told me that when he started out at Disney he took part in a drawing class taught by Marc Davis (the even-more legendary Disney animator). Of course, I asked right away: "What did you learn from Marc?"
Glen thought about it for a second, and then he said that Marc constantly repeated the phrase: "And again..."
Which I take to mean that there are only a few basic rules about drawing, and that you just have to keep reminding yourself of these same things over and over again. I don't think there are any great drawing secrets. You just have to keep reminding yourself of the basics, force yourself to stick with them, and apply them in an ever-more sophisticated way.
Composers don't sit around complaining that there are only twelve notes. They keep creating completely original works with the same tools Mozart had.
The problem with many of these simple tools is that there are a pain in the neck to make yourself do them. For example: silhouette value. As mentioned in the "Illusion of Life", this means that you stage everything in the clear, away from the body so that it can be read. Well, everybody KNOWS this, but they don't always DO it. Because it's a pain to keep working a pose so that is accomplishes this without looking stiff.
When I taught at CalArts, one night I started pinning up drawings with blacked-in silhouettes on the wall. One girl in the back sighed audibly and said "yeah, we know that already!" Of course, next week when she brought in her storyboards, I had to point out that she wasn't doing it in her sketches.
So anyway, a lot of what I post might seem basic and lame - you've probably heard it before. Hey, I know all this stuff too, and yet I always catch myself doing a sketch that doesn't do all it's supposed to. It's next to impossible to get all ten or twelve principles working just right in a sketch. So take a second look at this stuff, don't just skim it and say "Yeah, I know that." Hold your own feet to the fire. Are you really doing it?
I find I need stuff repeated over and over before my brain gets it. So I apologize if my posts seem too basic, or get repetitive. Consider yourself lucky if you have all this stuff down already. Heck, start a blog and teach the rest of us so I can get back to drawing and not blogging!
Of all the people I know, Glen Keane is one of the most enthusiastic about looking at this kind of basic stuff and talking about it. He goes to life drawing as much as he can and he's always throwing sketches away as he searches for a better way to do each one. He doesn't think of himself as great, (which, of course, he is) he just wants to get better. And ironically, that's how he got so good!
Below is a page from a handout I did a couple of years ago.