I get solo's called or take the opportunity every set. How I react depends on the tune.
If it's a ballad I'm usually playing fretless, I sketch the melody or create one off an arpeggio I let the mwah out of the barn and try to get my intonation as perfect as my limited fretless skills will allow by playing within the envelope. Folks like melody ...
If it's a country tune and I can get away with it and I haven't usedit recently steal the lick from "These boots were made for walkin", use that as the intro to a more advanced walk over the changes.
If it's a blues tune with a walk, I just keep on walkin'. ZZ Top style shuffle (LaGrange) I just keep on shufflin and look at the guy who called with 'what were you thinking, we need to talk look'.
If it's a jazz tune...I just keep reading and wonder, jeeze why did they all stop ? I did attempt to fit 'In Walked Bud' into a solo break in 'Autumn Leaves' once... It only took me 3 times around the head for the other folks to figure out where to jump in though... The beauty of an open mic jam! Probably should have sketched the melody and called it good...
If I'm feeling stale or don't know the changes that well or just am not feeling it... (Hey, it happens...) I turn to my drummer Jose and we play of each other a bit. I tend to play behind him so I may fall back further and just sketch the notes of the line I'm playing in the tune. He's always ready to go and is always a little ahead of the beat anyway. I just try to keep it funky. Personally I would rather listen to solo drums than solo bass anyway...
I do have a couple of stock turn arounds that start on the root way up high and then flow through the 3rd below ending on the dom 7. - which starting on the 5, in a 1-4-5 lands you the root of the 4 I adjust the line to end up on the 3rd of the root, chord that with the root an octave down, then walk back through the 5.
The problem with the stock lick approach is if you play in the same rooms a lot (I do) then your lick gets old ... So I try to mix it up an bunch - other than in the ballads. Those melodies can become part of the tune.
Mostly I try hard not to mess with the groove or the context of the tune... Referring to the melody, or a classic lick from the genre, working with your drummer to keep it funky, not playing a flurry of 16ths, unless it is in context - will keep you employed.
Sub-note... I play in commercial settings for the most part, nothing experimental, very little jazz. We do acoustic versions of classic covers, rock, pop, country, 'grass, blues, swing... So after not messing with the blues, for me, the other rule is don't mess with or lose the audience... Don't wank in other words. Works for me, might or might not for anyone else...
