"NEVER sing a song which you know someone does regularly."

I'm not so sure about that one. We don't have a problem with that at the clubs that I go to. In fact, on a number of occasions someone's sung a song which others have enjoyed so much that they've been stimulated to go away and learn it themselves. Nobody owns a song, and it actually becomes very interesting to hear how different people interpret and sing/play a particular song.

This does, of course, all have to be done with respect, and if I'm aware that someone gets a special pleasure out of singing a particular song, then I'd be considerate enough not to do it before them on every occasion.