There are two ways that I have sketched and I'll present them here. I began by simply using a #2 penicl and a circle. I eventually worked up to using a set of sketching pencils in the following ranges:
HB, 2H, 4H, 2B, 4B. Here is basic guide for items you need it your doing pencil/graphite on white paper. A Clipboard to draw on. A dim red observing light to illuminate the clipboard. Paper prepared in any of the following ways:
1. Blank. 2. Prepared with predrawn sketching circles. 3. Copied or preprinted log sheets. 4. Copied or printed or traced starfields (I recommend if your doing this to print off a prepinted map of stars with the circle for the eyepiece your using. This allows you to focus on drawing the object). Then a HB and 2H pencils.
Pen for notes, I recommend writing on the backside not on the front as it looks more pleasing. Blending stump or tortillon. Choice of erasers whether art gum, eraser pencil or kneaded. Eraser shield used to constrain erasures to a small area. Pencil sharpener or lead pointer. Sandpaper block used to hone the point of a pencil, blending stump, or tortillon.
Jeremy Perez over at his sketching site, The Belt of Venus has a great tutorial of how to use these items. It is located at this link. It is a video of Jeremy sketching M81 and M82 but the principals would work the same with a nebula or similar region. Jeremy to me is one the masters of not just sketching, but of capturing exactly what he sees at the eyepiece. Also at his Belt of Venus site Jeremy has a wonderful resource for Graphite on White paper located at this link.
Here are some images of materials you can purchase here in Utah at Hobby Lobby if you want to do this method. I have a case to hold my pencils and on the left side of the case are my sketching pencils. On the right, the blue are drafting pencils that hold sticks of lead and that come with their own sharpener to sharpen the lead. I like the drafting blue pencils as they are easier to use and hold. Next to the blue drafting pencils are my blending stumps. Below the case you can see an eraser that I use. Next to the case is my white sketching pad. I use to use a compass and make a circle but I personally find it more liberating to simple sketch on the paper. Here is a sandpaper sharpening tool that allows you to sharpen a pencils, or a blending stump. On the bottom of the sketching pad are two kneaded erasers in two different sizes. I prefer the larger size because it allows me to form it as I want. To the left of that are more blending stumps an a couple of tortillons which can blend also. Under that package is a chamois cloth that also helps in blending and removing blending marks.
The other method, which is the only method I am currently doing on my own sketching is called the Mellish method. It was developed by Scott Mellish of Austrailia. You can see Scott's work at Astronomy Sketch of the Day at this link and in this link. Scott, unfortunately, passed away at age 46 in April of 2011. Another wonderful observer who Scott had shared his technique with, Alexander or Alex Massey, actually got the word out to the astronomical world on the Mellish method of sketching. Alex made this tutorial over at Ice in Space at this link to the site.
The Mellish method is using a dry paintbrush to paint on the pastel to black paper. You use a white pencil or pen to make your stars, I use a pencil and then the brighter stars I come back later and make brighter with a white ink pen. I'll post images of what I use in a second. I recommend that you also look at these links if you want to do the Mellish method as posted in Alex's article.
Layering in the Mellish Method
here are some images of the items I use in my sketching using this wonderful method.
In the image above you can see, going from right to left the following. Sandpaper that you put the pastel down on to pick up with the paint brush. I got a thinner sheet of fine sandpaper from Lowes. Underneath that is a chamois cloth I use for this method to thin out pastel if I put down too much. Next to the sandpaper are two white pastel pencils that I get for putting down stars. I use the pencil to mark all my stars, and then a white ink pen which is laying in front of the pastel pencil and paint brushes I use the white gel ink pen to make the brighter stars brighter and to record my information on the back of the black paper. Next to the pastel white pencils are three bags of paint brushes. I use a variety, and have a larger set of fan brushes for larger nebula and wide field sketches. I use a variety so follow Alex's recommendation for brushes on his link if your new to this method. Next to the brushes are my pastel chalk. I have two sets. I have a basic set that are in the sandwich bag that are made by the General and have a white pastel, a light gray pastel, and then a dark grey pastel. The Green box is filled with a large variety of white, light and dark gray pastel that I use the most as I like the variety of colors it provides based on the object I am sketching.
Here is my sandpaper and my white pastel pencils with the sharpeners down below. I LOVE the sharpeners and the pencils.
Here are the pastel white pencils, and some of the brushes I use.
Below you can see the White Gel Ink pen I use, the eraser, one pencil sharpener, though I prefer the ones in the white pastel pencils. One of the pencils is out also.
Here is a close up of the white gel pen I use.
Here are my group of 3 pastels from the General and my Soft Pastels of white to various grays. They were on closeout and I gambled and bought four of them so I am set for some time!
Here is the gallery Artist's Soft Pastels in Greyscale.
The last thing you need is black paper. I get a type of black card stock that works well with me as I like that the paper really never bends unless I bend it.
There you go. That is what I use to do the Mellish method, well basically. I have a couple of items not pictured that I use also. I hope this helps.