So, when my boyfriend was teaching me how to “jam” with him while he played guitar, he encouraged me to turn the tv on and try to play or harmonize with the music on commercials. That’s how he learned how to jam with new band members. I’m still learning, so most of the time I can play a melody and jingles are pretty short and easy. I like car commercials because a lot of them use rock songs that are familiar to me.
With violin I find I am very structured too and don’t like to improvise. Since I play classical music, that isn’t a problem because we rarely ever improvise. However, I also sing contemporary a capella and I find trying to spontaneously sing harmonies to pop music is just as effective for developing the ear for violin.