A great article on gamegrene.com, The Ten Commandments of Priceless Players, about what players should do in an RPG. I haven't seen them all set down in one place for ages.
Well, it's a thin line really, obviously you have to act as your character, that's the most important point after (overall) having fun. However there are people who will knowingly and gleefully break the plot just 'cos they can and will avoid plot hooks or do bad things to them. This kind of behaviour should be discouraged, strongly.
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