The Hacker News welcome message
http://ycombinator.com/newswelcome.html
gives an overview of the community experiment here, summarizing the site guidelines.
http://ycombinator.com/newsguidelines.html
One of the guidelines is to prefer submitting original article titles:
"Please don't do things to make titles stand out, like using uppercase or exclamation points, or adding a parenthetical remark saying how great an article is. It's implicit in submitting something that you think it's important.
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"Otherwise please use the original title, unless it is misleading or linkbait."
The Hacker News FAQ
http://ycombinator.com/newsfaq.html
gives some additional details about how Hacker News is administered. The welcome message distills the basic rules into a simple statement: "Essentially there are two rules here: don't post or upvote crap links, and don't be rude or dumb in comment threads."