Complex sentence: He has often said that joining a rock band caused him to develop poor playing habits, one of which is awkwardly holding his violin to the side of his head in order to hear himself better through the guitar amps and PA system.
Split into simpler sentences: He has often said that joining a rock band caused him to develop poor playing habits. One of which, is akwardly holding his violin to the side of his head to be better able to hear himself thru the guitar amps and PA system.