Well, it's a fact that most galaxies look alike through the eyepeice. But there are special attributes to an object you can note that make the observation more precise. Most galaxies are elongated. Just swing the telescope back and forth in East-West direction to indicate where North and East is in the field, and note a rough estimate of the angle. Often this is different for different sides of the nebula.
Dark nebulae are propably the least observed objects.
Well, most dark nebulae lie in front of the Milky Way or some bright nebulae, and therefore block out the light. Thus it's possible to see them, and beleive me, it's much fun observing them. Most dark nebulae are better for photography, but many of them are infact very easy to spot. Definition - The same as for bright nebulae. Many dark nebulae will show faint whiscs in some directions.