I originally trained as a draftsman (draftsperson?), and sketched every once in a while when the mood struck. (ranged from pretty good to awful, as I recall, except for horses, and more horses...)
I jumped to computer graphics a couple of years ago, and, sad to day, my sketching ability/practice time has been almost non-existent lately. I, too, find that for many of the things I want to do, I'm going to have to re-learn drawing, at least for the preliminary sketch aspect of the work. There's just so much I can't do as well as I'd like when I'm working totally without prelims.
I also know that the only way I'm going to do it is to open up time to simply draw (eek - not on the computer?), and put an extra wastebasket or two in close proximity, wherever I am. For every drawing that's worked from scratch, two or three or more are, well, awful.
One of my worst problems is that I've known Kelly Freas for a number of years, and watching him pick up a set of magic markers and simply create one wonderful thing after another on the spur of the moment without ever blowing it - well, that's a difficult act to even consider following. (I know he's been doing it as long as I've been alive - that doesn't, somehow, seem to count)