One of the things I do with my beginning drawing students is first have them
experiment with how light-to-dark they can make an HB, 2B, 4B, and 6B pencil.
On this same sheet, they also have to draw some simple objects and shade them
in - sphere, pyramid, etc. Next, I have them draw three vases. Small, medium
and large. The largest has to be the lightest and the smallest is the
darkest. They have to use all of the graphite pencils and create a total
value drawing. If there is any line showing I keep sending them back to work.
Since the vases are made up by them, it removes the idea that it does or
doesn't look like a vase in front of them. Makes it be all about value. After
they finish this, I have them drawing a still life of about 10-12 objects
that are all white. ( If necessary, I've spraypainted some objects white. I
usually keep a can handy in case I need a new item or something gets
misplaced or broken.) I darken the room a bit and use spotlights to
emphasize the light/ shadow. Since they aren't making decisions about how
light or dark a color needs to be they can focus on value. This must also be
a value drawing. No lines but areas of light and dark. Despite the fact that
they seem intimidated initially, they frequently mention to me later that
this is a project that made them think about value and gave them a drawing of
which they were proud.
Hope it helps. Good luck. Monica