Reddit reviews Instant Songwriting: Musical Improv from Dunce to Diva

Hey! I've done longform musical improv. The building block of it is the scene-to-song. Basically, learn how to push your emotion or character deal into a song moment. If you watch a lot of musicals, you'll start to see what I mean. After that, you can work on song structure (verse-chorus-verse, tagline, etc.) and then string the scenes together however you'd like (as a Harold, a montage, a single long monoscene, or narrative).

To that end, I recommend:
• Instant Songwriting
• The Improv Comedy Musician (For your accompaniest mostly)
• Musical Direction for Improv (The author has another older book but it seems to be out of print. I think this one's an updated/expanded/revised version of that book though.)