That's the question for me today . . should one even rehearse? It's a bit of a contradiction in terms. If my gig is advertised as free improvisation, for me that means real life in the moment coming up with something out of nothing, genuinely creating on the spot, starting with no idea of what my hands will play. This is what I love to do when alone in my studio as it always surprises me, regenerates me, makes me feel great. But live . . come on!
Maybe one day - but now I feel I I need a fall back plan, a few chords I can rely on to get me out of a jam should the Almighty not show up on the night. So as ever, a compromise seems to be the only thing. The middle ground.
Apart from the wonderful Kenney Werner there's not a lot out there on this subject. My method is this. Shut my eyes, open just my ears, and randomly press my fingers on two or three notes on the piano.
Breathe, and play a few more notes, listen, listen listen, decide to love every sound that comes forth, Refuse to wince or dislike any of them, all are there for a purpose, all are sent to form a pattern of sounds that will become music, if I allow. Never feel pressure, allow vast amounts of space and silence, allow it to be really simple, wait for the melody to emerge (there may not be one), accept that. Sit back and be aware of the urges to change key / rythm / inversion . is it easy or is it forcing? cultivate awareness to distinguish between wanting to sound good, and loving what is coming out. Always choose loving what is, tending to it, developing it, nurturing it, repeating it, being with it.
So easy to talk the talk . . another thing to play the play!