Answer:
Well, you look at the "chord changes" which are chords that either the piano or guitar player plays. You use scales that are with the chords. For example, If the first chord is "F" major 7, I might play different notes in an F major scale ( f g a bb c d e f ) or f dominant ( f g a bb c d eb f) or the "bebop scale" which uses the major and dominant ( f g a bb c d eb e f) also use licks from other people you might listen to ( John Coltrane, Dexter Gordon, Lester Young, Sonny Rollins, etc.