http://www.webdiplomacy.net/rules.php#Rules
The rule is simple :)

It is polite (although not required) to tell people ahead of time that you are playing with someone you know.

As long as you do not break any rules, or treat your friend differently than other players for out-of-game issues, there should be no problems.

it is appropriate to tell other players if you know someone (like when i convince my housemate to play, we have an unfair communication advantage because we can talk in-house)

Being polite by letting people know before a game starts is as fair as you can get.

Also if you want to introduce them to the tactical side of the game, i highly recommend playing some of the two player versus variants like France vs Austria: see - http://vdiplomacy.net/variants.php?variantID=15

Thank you for the advice. Redhouse, I'm satisfied that I have complied with Rule 2, as nobody knows who is who (anonymous players) and he has not told me outside of the game (he doesn't live with me). I'm going to announce in game that I know another player.

well, may not want to announce it *now*, since everyone will then know which country you are...

thats a very good point lol

If I announce it now, he will know who I am! I was just thinking that as I typed inthe Global message!

Smart thinking. As i have had a few issues in the past i am well aware of this issue. I have a friend i frequently play with, but we only communicate in game and stab/attack one another a lot so it is no issue. The biggest issue is not to always ally with your friend, that can and will be interpreted as metagaming. once or twice, ok, but no more than average or situationally.

Usually, I suggest teaching someone by having them in their own game without you. That way you can sit over their shoulder and help them by hand holding the whole way.
If you aren't in the game, you aren't getting any extra information to give you an advantage, so you are being perfectly legal...
However, if you are in the same game, you can't hand hold and help someone because you are privy to information they may not know or could not know, which means you would be breaking the rule on metagaming.

I've introduced my brother-in-law to the game and played non-anon games with him. Same with people I know here at college. I simply make it a point to stab them. It teaches them not to trust anyone, including you, and they still learn the ropes of the game. So...for the record, if you're my friend in real life, don't ally with me.

diplomat- yeh yeh

we all know the "friend" you play with... that friend being yourself you dirty naughty boy

@Fk, i know the hands on teaching method is more useful than mere theoretical instruction, but i know too many people who tell people how to play, and effectively play a game by proxy through the person trying to learn.

I'd hate to think that someone wasn't learning because they felt like a puppet...

On the other hand pretending to be a puppet could be a useful strategy to gain information and trust of other players... hmm...

Bah, just jump in play a game and win it. Piece of cake. That's how I did it.