I'd like to ask what online behaviour is acceptable, and what is not.

My son (12 y.o.) is into this & has recently ventured into online play. I want to educate him on the nuances of playing this game online, what to do/what not to do, and to discern sporting from unsporting behaviour.

It would depend on what he is playing I suppose, but generally you do not want to get people mad, although people wont admit it, there are some strange people on the internet that dont have lives and well, you get the rest, I dont play all that much online, but I would just tell him to be carefull in what he says, and the way he acts-No mischief, dont know what they call it but there is a name for people who go into games and just try to ruin it for everyone else. Im sure he'll be okay though, there are also some very nice people online.