If one has been performing mock solo concerts for years, you don't prepare - you are always prepared. "Practice" Sessions, for me, are opportunities to perform. Every session is a performance, and not necessarily a preparation for a performance, but really a performance, even though there might not be an actual live audience there. An imaginary audience is always possible.
Still.... preparing for a real "public" solo performance or recording requires a certain advance planing: length of program, number of pieces, relative number of improvised pieces to composed pieces, etc.
You know, when one is as strong and secure as possible, then, when playing with others, we can actually elevate the other players and allow them to feel secure and confident that they can trust the musical moment and be free to interact, groove, respond, freakout, whatever the music desires.
Even though, I would love to perform a complete improvised program, I also love playing beautiful melodies and expressing myself through the melodies of master composers like Thelonious Monk, Duke Ellington and Billy Strayhorn. So, why not mix and match?
Regarding forms for the improvised pieces, I usually decide on-the-spot, from a group of forms, feelings, emotions, vibes, tempos etc., from the pieces that I have already improvised and or composed and cataloged. There are several "vibes" that we can choose from, like different tempos, vibrato, plunger, and others.
And then, utilizing the composers perspective......compose something (with the chosen vibe) on the spot. Fun!!
Like almost everything else in life, the more you do it, the better it gets.
If you are in New York tomorrow July 20th, come join me for my solo performance at ShapeShifter Lab in Brooklyn at 9:30PM.