Music as conversation:
My favourite soloists in music always seem to have an inate sense of what the other
instruments in a song are doing and how to converse with them in a meaningful way.
Even though they (guitarist) might be the prominent soloist in the band, they seem to be looking to play off something the bassist, drummer or keyboardist is doing underneath or to the side of them.
Melody playback:
Great guitarists always use the songs melodies and themes to help come up with
solos and lines. I like to learn some of the vocal melody lines at different locations on the
fretboard and sneak them into my solos, lines and riffs. Sometimes it helps to use melodic content
as your start the solo or as your move up higher on the neck and build to a high point in the solo.
Rhythmic changes:
Many beginning guitar players make the mistake of being too predictable. Lead lines that
always start at the top of the bar or always on the on-beat can often sound uninteresting
and unimaginative and leave the audience unmoved. It's important to mix things up with
lines of unequal length, starting on the off-beats and playing over the bar-line. Adding
triplets, rhythmic hick-ups and space between lines can add a fantastic amount of
dynamics, tension and excitement to your playing.
Linear vs. Positional:
If positional playing (in one scale form) is putting me in a musical rut or not working in a
specific song I will try a linear approach (playing on one or two strings). Sometimes
a small adjustment of that type will put you on a fresh path to new inspiration or
just on the path to what the song really needs.
Chord or Target tones:
Just as horn players and piano players love to play lines that include arpeggios, triads and
chord tones, many guitarist avoid this approach because it takes a fair amount of fretboard and
theory knowledge. A solution is to start with simple small triadic shapes on the 1st 3 strings and
highlight those in lead lines. A perfect example of this is the solo in 'Comfortably Numb'.
Phrases and sentences:
Way to many guitarist solo with musical run-on sentences. Try to leave some blank space
at the end a lick or phrase, like a period at the end of a sentence. I might try to play 4
phrases for an 8 bar solo or think of a solo as a musical poem. It will help create those
wonderful story lines we hear in classic solos.
Space or "Air":
Don't be afraid to leave space and air in your solos. Sometimes the best thing to do
when you want to play is to be silent and listen to what's going on around you in the
music. Try for 25% less notes in your solos.
I hope this helps you to at least begin to strategize and think about soloing in different ways.