Recently checked this book out of the library, you'll probably find it's about what you're looking for: "The Painterly Approach, an artist's guide to Seeing, Painting and Expressing" by Bob Rohm.
I'm with Flynn on this one... but I finally realized that, for me, the barrier to drawing was 'lost edges', that is, areas of smooth transition from one value to the next. Sharp, high-contrast edges, by contrast (har) were easy, but there's so much out there that isn't.
I wound up being enlightened by learning with a charcoal technique. You use sandpaper on vine charcoal to produce charcoal dust, which you rub into fairly thick paper (charcoal or watercolor paper). Then you draw (to make darker areas) and erase (to make lighter areas) and the blending is almost automatic, due to the fact that it's already charcoal there.
So you might use the chalk tool on a 'ground' of medium gray; force yourself to make areas, not outlines, with a few higher and lower shades of gray. I believe ArtRage comes with a seven-steps-of-gray color sample set.
Let us know what works for you...
WARNING: ArtRage can cause serious loss of time, and excessive smiling! Use with care! Frequently!
“All creativity is an extended form of a joke.” – Alan Kay