I (very rarely) say anything in dungeons, my way of showing respect to other players is doing my role to the best of my ability and pulling my own weight. I generally will only speak in a dungeon if I am specifically asked a question, i.e. while leveling a healer, tanks have asked me if I mind if they pulled big or healers specifically asking me to pull big when I am tanking. I will respond to that, but not really anything else. If someone is new I will offer them an abridged set of tips based on what they need to know to beat a boss. "Don't stand in this, dps that add when it pops, move here when this happens, win." Something like that.