@Michael – my teacher taught me about using passing notes in improvisation. Once you understand the logic behind the purpose of using passing notes, you have to go away and experiment with them to feel if they work or not for whatever piece you are working on – the whole point of improvising is its completely up to you, if sounds good keep it in. A tip from someone else (Seasoned pro), once you’ve done all the theory and practiced it over and over, then just forget all the theory, put on the backing track and jam along to it. Whatever is buried in your mind should start coming out without thinking about it.