There aren't so many things I regret, but the one music-related thing I would tell my younger self is "Learn to sing!". Most musicians can sing to some extent. Early on, I was in a band that did a lot of pop tunes that require at least two and three parts. The guys told me I should sing but I said I wanted to concentrate on playing. We were playing six nights a week in a club, a perfect opportunity to practice and get better. I now find that to have been a big mistake! A few years later, I got an important tour and I didn't know that my friend who got me on it had told the leader I could sing! That was proven to be "fake news" in the studio, after a valiant effort at harmony part. Had I done more during those club days, I could have certainly done the harmony parts, as they didn't require a great voice, just a decent sense of pitch and time.