After sketching the surrounding star field, load a small blending stump from a patch of graphite outside your sketch circle. Draw the borders of the galaxy’s dust lane by holding the blending stump almost perpendicular to the paper, using its tip. Then, angle the stump and use the side of the tip to draw the remainder of the galaxy.
My second example is the most massive globular cluster in the Milky Way, Omega Centauri (NGC 5139). Edmond Halley discovered it in 1677. It’s a whopping 150 light-years across and contains more than 10 million stars. At magnitude 3.9, this naked-eye object is a treat through all telescopes, but it really knocks your socks off when you use large apertures because of the sheer number of resolvable stars. Make sure to look for (and sketch) the streamers of suns resembling claw marks in the cluster’s southwestern quadrant.
Again, first sketch the surrounding stars. Include enough of them to position the cluster. Then, starting with Omega Centauri’s bright center, use the edge of a large blending stump to build up the object’s brightness.