Not letting personal feelings get the best of you in arguments or confrontations.
Be unbiased to everyone you meet.
Always follow the rules and treat everyone with respect.
A good overall knowledge of the game subject and of other player's feelings. (Being a "jerk" as a GS is just a no-go)
Appropriate Grammar. You are a professional volunteer of a online game, use normal words and not text speak/constant emoticons, this is not YIM, or AIM, or whatever.
Always follow rules and regulations, if there is a grey area, always seek a second opinion before you post something.
Make sure you have fun- it is a exciting and enjoyable position, if you act like a wet dog, people might not come to you for any problems, or could become intimidated.
+ Lots of more things I could put, but way too lazy.