How about a willingness to admit and learn from mistakes. I don't claim to be a great DM but I have fun, the players have fun, and everything else is just gravy. I'm just finishing up my first long term campaign (a little shy of the 2 year mark, playing once a week with a brief Vampire break) I've made some mistakes - npcs stealing their thunder, too much treasure, being too lenient with players using oddball third party rules - but as long as the communications lines stay open and everyone is willing to forgive me and let me fix things, in game if possible, out of game if necessary, when I mess up everything stays cool. Plus, learning from those mistakes are what has made me the overwhelmingly adequate DM I am today.