I like to think of myself as "artistic" and I did manage to pass my drawing classes in college, but I don't feel very comfortable sketching garments for submission or design, until now. Probably a year ago, I got this "average woman" picture from Threads Magazine's website I don't know if it is still up on their site, and I don't know where on the site it is.
They also had toddler, adult man, and a few other diagrams. I printed it out and now I put it under tracing paper. I sketch on the tracing paper, on top of the diagram, and Viola' I have a sketch that is in general proportion to the person I am designing for! I add lots of notes around the sketch about yarns, stitches, areas of interest, and suddenly, I can see it.