Some of these I learned from trial and error, some from reading other books, websites, and listening to other people. I think all ideas are worth considering, though as I learn, I may find better ones than some here.

1. Draw what you see, not what you expect to see. Sounds obvious, but it is easier said than done–knowing what a galaxy is supposed to look like does influence how we draw it–that temptation has to be resisted! I often forget to put spikes on stars, knowing they are not really there, for example.
2. Use any aid you can to place stars close to where they belong–use a reticle eyepiece, imagine graph paper or a clock face on the field of view, look for geometric figures you can copy such as triangles.
3. By drawing brighter stars before dimmer stars, it helps you draw them brighter/dimmer as they should be.
4. After you finished the sketch at the eyepiece, look again–I have often seen things I missed that way.
5. Consider a clock drive–continually adjusting the scope gets to be a bother.
6. To “dip” the smudge stick, put pencil or charcoal marks on another paper or even outside the field of view, then rub the stick on the marks.
7. Before using the smudge stick, test it outside the field of view or on another paper–if too dark, rub it on paper; if not dark enough, “dip” it again.
8. Start each sketch mark lightly–easier to darken something too light than to lighten something too dark. Even start with pencil not touching the paper while making sketching motions, and slowly bear down till you see the marks appear.
9. If you are “drawing challenged” like me, draw complicated things multiple times, or take a complicated piece of the sketch and draw a magnified version of that piece. Then inside at your desk when creating the final sketch, integrate the multiple drawings into a single more-accurate drawing.
10. Take care to note that the field of view may rotate over time.
11. Try to get a “gestalt” of the image in the eyepiece–that will help you decide what the important features to sketch are, particularly for something too complex to copy down faithfully (such as M24 (countless resolved stars) in a wide-field eyepiece with medium to large aperture).
12. If you draw a nebulosity before drawing stars in it, smudging will not ruin the stars.
13. Conscious effort is needed to make the stars circular–make sure the pencil moves in tiny circles.
14. Make notes at the eyepiece about those things you can’t render faithfully–such as colors if you only have black-and-white pencils. Then, you can re-sketch inside and use the notes to make it a faithful representation.
15. There are several goals to sketching depending on your needs and tastes, some of them somewhat conflicting–sketch to recognize it later in a field of view, sketch to compare with star charts to check you have the correct object, sketch to look like a realistic photograph, or a sketch to show what has changed since the last sketch. Keep your goal(s) in mind and try to make your sketch satisfy them.