What is the process that great jazz players do to write strong jazz lines?
In addition to knowing your language (music) most jazz musicians have
transcribed solos and learned to play them as part of their studies.
In addition, focusing your work by making sure you listen to
everything that you play so your ears are matched to your knowledge
of music theory is vital.
How do you sustain a line, technically and conceptually, so that it tells a
story, not just runs scales, however hip they may be?
Think about story-telling devices. You have protagonists and antagonists
(themes and counter-themes), key players and peripheral characters
(main notes and embellishments) and characters are put through various
situations to develop their understanding in the story (playing through the
changes.)
You can use literary devices such as the "Notion of Return" or coming back
around to a thematic idea or riff in different parts of the solo.
Building from simple elements to more complex elements and climaxing
towards the end of the solo are all ways of creating a kind of musical
drama that can be very satisfying.
Mostly, try to follow the story yourself as you play!
TUNINGS
Why don’t Jazz Guitarists use alternate tunings?
Some jazz guitarist do work with different tunings, but tuning your
guitar to a chord can limit your ability to quickly change into the
many chords and keys required in most jazz tunes.
A more generic tuning is more effective for multi-key playing.