I started with a basic pencil sketch on inexpensive sketchbook paper:

Then I developed the first layers of mid-tones using a 2H pencil:

Then I added some initial shadows with a B pencil:

After that, I used a 6B pencil to create the darkest darks:

Finally, I used a 6H pencil to nuance the mid-tones, and a kneaded rubber eraser to mark out the highlights:

Here's a scan of the finished piece, and my reference image: