Set an object on a table and shine a flashlight in one direction, observing how the shadow casts. As you pull the flashlight away, the edges of the shadow become sharper and as you place the light closer the edges become softer. Play with different shadow effects and then choose the most interesting shadow for your drawing, then draw your object.
Create a tonal value chart to base the light and dark shades on. Start by creating a rectangle with eight boxes. In the first box, using your pencil, lightly fill in a light shade of gray. In the next box, fill in darker shade of gray and continue filling in the boxes with each box a shade darker. This will help determine the value range for the drawing and will help prevent it from becoming too flat.
Shade in the drawing where the object is in the shadows. Refer to the tonal values to create a balanced and pleasing composition. The distribution of light and dark is just as important in as the composition itself. Use the eraser to lighten areas if needed.