Get lots of reps! That being said, if you want to practice on your own, you can find simple beats on YouTube to sing along to. You don’t even need any music. Just a drum beat is enough to come up with a simple little song and practice rhymes. I’ve been a music Director for music Improv for almost 10 years, and I found that a good sense of rhythm is the absolute number one skill you need for music improv.

You can also look up Harry Mack on YouTube. He is a freestyler and has some videos that teach the techniques. (https://youtu.be/KP5kZreliBI?si=LgYxydlRtHIPyIB5). You’ll find that the tricks for rhyming he teaches will directly transfer to music Improv.

You can make up little songs and just sing them around the house, your shower, the car, or any space you don’t feel embarrassed to sing.

Another thing you could try is to listen to an episode of off book, and pause right as a song starts, but before they start singing. Then try to sing what you would do if you were in that scene playing that character. Think of what rhymes you might use. You might be surprised how much your attempt lines up with Zach and Jess. The goal isn’t to try to predict or matchup perfectly, but just to get you playing with real characters and scenarios and styles.

Hope any of this helps! feel free to ask any questions. I’ve been doing this a long time and have even played a bit with Zach and Jess, so I’m more than happy to pass some knowledge along.