Look for the oldest piece of technology you can find in your house. Really old – not a computer or iPod, or anything with a screen! Find something like an old typewriter, or a gardening tool. Place it next to a window or strong light in order to get well-defined shadows and highlights. Then zoom in on one particular portion of the tool and then draw it, with FULL VALUES.
Sketches without values (line drawings) will not get full credit.
See below for a couple of examples: