Check out this interview with Pierre Bensusan from Acoustic Guitar magazine. My favorite bit (Pierre speaking):

I have had the great fortune to play with a fantastic improviser, Didier Malherbe, who plays woodwinds. And he taught me two things. He said, “First, you are not here to be unhappy onstage. You are onstage to be happy and to share this happiness. Turn this happiness into music and through the music give it to the people.” The second thing was, “I try to have my head as empty as possible, so that things can come to me, penetrate me.” When you expect something, your head’s busy expecting! You’ve closed the door to something that could happen. So this is the attitude of the great improvisers.