Before you post, check the "new" page first. It takes just seconds to notice that a headline has been (over)posted 10 times already, and it should be obvious that we don't need to see it yet again. The repetition only makes it harder to find unique new stories.

Then there's the question of relevance. A story can be "important" and still not be "hacker news". Post things that are relevant to this site; anything that's better covered on a general news site doesn't belong.