When ever I started a new drawing class the first thing I require the students to do is surround themselves with great drawings...now with the internet there is no excuse for lack of source.. The Morgan Library in NYC is one great drawing experience, not only for their collections but for the excellent environment it provides for the viewer. Today (October 2, 2009, through January 3, 2010) they are opening with a series of drawings - Rococo and Revolution: Eighteenth-Century French Drawings features more than eighty exceptional drawings almost exclusively from the Morgan's renowned holdings. The exhibition includes Antoine Watteau, Jacques-Louis David, François Boucher, and Jean-Honoré Fragonard, among others. Go to the Morgan's exhibit links and play with the zoom on each drawing...look for how the lines describe the form in the placement of the shading.
Antoine Watteau (1684–1721) Seated Young Woman, ca. 1716
Black, red, and white chalk
Purchased by Pierpont Morgan, 1911; I, 278a