I use a modified draftsman approach in that I ink with two or three
general line thicknesses. Of these, each type will vary in width,
but generally never be thinner than the thickest of the next category
down. The lines for organic or living things are "cursive," or "live"
lines. Inorganic, technical subjects, and things seen on monitors, are
inked with a "dead" or constant width line. Here's a familiar picture,
showing the technique in action. In order of thickest to thinnest,
the line types I use are:
I tend to not use cross-hatching, because I can never make it look
sufficiently tidy to my taste.