Step 1 — Decide what to sketch
I’m probably not the best person to be telling this to anyone, but at some point you have to stop admiring the view in the eyepiece and get to work. I’ve let too many wonderful sketching opportunities slip through my fingers because I was playing tourist along the terminator. Begin by scouting out a primary target to sketch and observe its placement within the surrounding terrain. If this is your first attempt at a lunar sketch, look for a single, well-defined feature and aim to keep it simple. Before I actually begin sketching, I often take a quick eyepiece shot with a digital camera so that I have something to check my sketch against later. I should note that I never use the photograph to grab details for my sketch that I might have missed at the eyepiece.
All set? Got your medium-lead pencil for details and a soft-lead pencil for shading? Got your art eraser and an unlined notebook? Then let’s get started.

Step 2 — Make a rough outline of your primary target
Believe it or not, putting the first pencil mark on the page is the toughest part of this whole exercise. Lots of people get very uptight about making sure that first mark is absolutely perfect. I can think of better ways to get an ulcer, so here’s how to get around it. Make a fast, light pencil outline of the crater. You don’t need to fuss over it because you won’t be keeping it. Compare what you’ve just drawn with the view in the eyepiece...then erase the outline. If you are anything like me, nine times out of ten it wasn’t right anyway. Now that you’ve dirtied up the page a bit, your mind will be free to begin sketching a more accurate rough outline with a more confident hand. This will be the basis for your final sketch, so log the start time into your notebook. If you are having difficulty keeping things in proportion, establish a few landmark points on the page and connect the dots. It seems to work for me. The rough outline should take you no more than a few minutes.

Step 3 — “Time-stamp” your sketch with shadows
Houston, the clock is running! Keep an eye on the time. Because the day/night terminator advances noticeably across the lunar surface, shadow shapes will change fairly quickly. As a rule of thumb, plan on defining all major points, including the darkest shadows, within 15 minutes.
You need to work carefully, but quickly. Sketch only what you see, not what you think you see. Refer constantly to the view in the eyepiece to make sure you are getting things right. Once the dark shadows are in place, the Sun angle (and therefore your sketch) will be “time-stamped” for posterity. Again, log the time in your notebook.

Step 4 — Add shading and context
Your sketch is about to “come alive” with depth. With your softlead pencil, begin shading in the tonal differences on the crater floor and along the walls. The brightest sunlit areas will be the white of your paper. You may be surprised at how, with even a bit of shading in place, your sketch suddenly takes on a more natural, three-dimensional look. During Step 4 I also begin to define the context of the crater by sketching in a few of the closest adjacent features. Believe me, it is easy to feel overwhelmed by the sheer amount of interesting detail available in the immediate vicinity of a crater, so for the moment restrict yourself to adding just enough lines and shadows to give a bit of framework to your sketch. Until now the crater has been more or less “floating in space” on your page. Your goal here is simply to anchor it to the surface of the Moon by establishing where it fits among a few surrounding features. At this point you may well decide to add nothing more to your sketch. You still need to make some final adjustments to the tone and contrast (Step 6), and annotate your drawing with the pertinent observational details (Step 7) - but you should now have a pleasing observational sketch of a lunar surface feature in your notebook. Well done!

Step 5 — Extend the Sketch
If you are up to it, extend the limits of your sketch to a few more of the nearby features, including the terminator or the lunar limb if they aren’t too far away. Again, start with a quick outline and establish the dark shadows as soon as possible so that you don’t inadvertently create multiple Sun angle time-stamps across your finished sketch. I ran into trouble with this myself with Gassendi. The sky clouded over right after Step 3, when I’d just time-stamped the shadows onto the crater. By the time the sky cleared up enough for me to sketch in some additional features more than an hour later, details toward the terminator that were previously in shadow were now blazing away in the morning lunar sunlight. This discrepancy is glaringly obvious if you compare the sketch with my very bad digital image (you see now why I prefer pencils to pixels). Many of the highlights sketched in near the terminator do not appear in the image I snapped at the beginning of the sketching run.

Step 6 — Finalize Tone and Contrast
You’re almost done. Take a few minutes to compare the tonal values in your sketch with what you see in the eyepiece and adjust the shading as required. Use your art eraser to pull out any bright highlights that got drawn too dark. Now, look at your sketch with an eye to the overall contrast. Are your whites white? Are your darks dark? How does the overall effect compare to the eyepiece view? Probably the easiest way to establish the final contrast in your sketch is to make the shadows as black as possible. Most people tend to sketch far too lightly, probably because they aren’t confident about what they are doing with the pencil. One of my great frustrations is looking back through my early logbook sketches and seeing all those ethereal images of galaxies, nebulae, star clusters, lunar craters.... They look like they were drawn by a timid ghost using near-invisible graphite. So be bold with that pencil and really establish those lines and shadows. Now that your sketch is done, log the finish time into your notebook. All that’s left is to add the observing data.

Step 7 — Record the Observational Details
Remember that you are creating an observational sketch. The details of the observation are all-important, so include them as part of your drawing. You’ll want to note the date and time(s), sky conditions, temperature, what it is you have sketched, the observing instrument and eyepiece you used, and a directional arrow (missing from my Gassendi sketch - yikes!) to indicate north, south, east, and west. Having this information as part of the finished sketch helps me reconstruct the observation even years later. I also happen to like the look of a working sketch that contains this data as part of the overall image.