How Not To Be An Internet Troll
Stay on topic. This seems simple, but it is quite easy to read a post that mentions either someone or something that triggers a strong emotional response. Then acting on that response, you post your opinion on that someone or something, even if your opinion is not really on topic. For example, locally there was a big, public debate about the school calendar, with certain board members vocal about opposite sides. For several months after the debate, if a news article mentioned the name of one of the school board members, there was inevitably one or two comments that ranted about the school calendar regardless of the topic of the article. Do you know how annoying it becomes to read an article about renovations approved by the school board, only to find the comments sections overrun with the same arguments about the school calendar? The trolling leaves no room for appropriate discussion.
Keep it impersonal. This means no name-calling, no insinuations about someone's intelligence, bodily functions or origins, and no comparisons to either inanimate objects, bodily parts, or other animal species. Yes, I realize that someone just made a comment that only a dim-witted, Justin-Bieber-loving rock fart would say, but you really shouldn't call that person a dim-witted, Justin-Bieber-loving rock fart. It just isn't nice.
Corollary to rule 2: Sarcasm is all right, as long as it's not personal. If someone accuses you of attempting to cut them out of a conversation, ruin their life, or some other insane sounding accusation, try responding with "After years and years of research, trying to determine the best way to remove you from the conversation, I find your comments validating. Thank you."
Don't needlessly soapbox on a thread. By "soapbox", I mean don't simply repeat your current rant even if what you are posting on might be appropriate. No one likes to be preached at.
Don't act like every conversation is a contest for who scores the most points.
Be nice. I know that this sounds a bit simple, but if you always try to be nice, chances are you won't accidentally be a troll.