I know that this is kinda "cheating", but for students who are unsure
about their art skills--this is a boost because it is so successful.
Drawing from a white still life can be so difficult to begin with. I
first have them do a ten-value value scale from black to white with a
pencil--no smudging. Then I have them bring in a black and white photo
that I chop in half. They glue half down on drawing paper, and copy the
other half to fill in the rest of the picture. They can grid if they
want to get proportions right. I do not let them smudge. They all turn
out well, although at the beginning they draw it too lightly and you
have to push them to add all the value. Once they do this, the still
life might be the next move.