My view of good etiquette is that you should be cheering for the beauty of the game, not for the ugly parts or not to be ugly. A good spectator encourages their team, but can also appreciate a fantastic save by the other keeper or a beautiful shot. If something goes wrong or there's a bad call, an "awww" or momentary "that sucks!" is okay, but rants or expletives are not.
Be a good sportsman, don't do or say anything you wouldn't want to experience as a player, and always be a positive force, not a negative one.
