Along the lines of the PM's that come to new players, I think they should add to the one about "first move" or "second move" a few eitquette points. They can say, the members of CC encourage you to follow these rules of etiquette when you play...
Then I'd like to hear what "niceties" the rest of you would add, but let's maybe just try to 5 +/- really good ones that are pretty easy to agree on. Here is my list:
1) Do your best to make all of your turns. Quitting a game just because you are losing makes everyone else in the game wait around.
2) The person you are playing might be younger than you think... try to avoid profanity in your game chat (obviously reciprocating when the other guy b*tching that you killed his army is ok if you like that sort of thing)
3) In freestlye games/real time games, let your opponent know if you have to take a break before the game is over. If someone askes you "rt?", it means play real time.
4) If you want to form an alliance with someone in an non-team game, announce it in the game chat. If you plan an alliance, it will help the integrity of the game if you limit it to a reasonable number of turns.
Maybe this is lame, but it's maybe worth trying since the emails go out to new members anyway...