Vary line weight

Some artists prefer to build up
the weight of their lines by going
over them a few times. This is especially true for artists who
use thick lines in their work. Think of building up lines as three
parts to each line. The first part is almost like the main body of
the line and it will be filled in. The other two parts are the outline
of the line. If you imagine two lines that are running parallel, and
then filling in the gap between them. This will allow you to work
with smaller needle groupings and still be able to have a variation
of line weights throughout a piece.