I honestly dont think ahead. Since I'm not a theory guy, and rarely play by memorizing chords or hand positions, I just go with the flow.
But now that I'm geting into some "phatter" stuff, I'm paying more attention to what I have to play next.
Also, if I'm really taking the time to learn a song, then I'll think about what comes next, but after I've practiced it a bit, it I'll play it like second nature
And like CJ said, When you are playing under the anointing of the Holy Ghost, you dont know whats gonna happen!