I am unsure how to do deadmines on WoW (Lvl 15-21)?

I have done deadmines a few times now and I think it's great, but at the beginning, when you need to accept the quest to kill the bosses, it isn't there, it just says "There are always new things to explore" (I did accept the quest the first time that I did it, so can you only accept it once?), but I don't know whether I am doing the right thing to get the quest. Also, throughout the first time I did deadmines, I had to accept new quest to kill the next boss along, again, that doesn't happen now. Then, at the end when I have defeated Admiral Ripsnarl and Captain Cookie, the Lieutenant just arrives, kneels down and says, "that's just the way the cookie crumbles". Nothing happens then so I teleport out of the dungeon and leave the group, then select Dungeon Finder again. Is this the correct way to do it or I am doing it wrong? Any help appreciated!