My top 10 list
- Reads and understands the group and adjusts the game to suit.
- Plays to their strengths. Good at accents? Go for it. Every accent sounds like an annoyed Elmer Fudd? Maybe try something else.
- Varies the pace and types of encounters and sessions.
- Improvises when needed. No plan survives an encounter with the players.
- Gives the players meaningful choices.
- Doesn't force the "correct" way to play on their players, accepts that some people enjoy different aspects of the game.
- Know when to look up a rule and when to just make a ruling and move on. Try to be consistent in how you make decisions but don't bring a scene to a screeching halt for flipping through pages of the book.
- Understands the difference between setting the scene and boring monologues. Describe enough to give an accurate picture, don't go into details describing the sword above the mantle unless it matters.
- Understands the campaign world and is consistent on how they describe it.
- Is always willing to learn and improve.