- news should be new; and
- news should come from the original source.
You should only post news that is new. It is only valuable information to other traders if they haven't seen it before. This means that you should check the date of the article. If it isn't dated today, don't bother posting it on the forums.
New news also means that it hasn't been posted on the forums before. Before you post, just check the first page or so of the boards and the relevant moviestock page to make sure that someone hasn't gotten to the news first.
When you do post news, you should post the original source of the news. This is because there is usually more and better information in the original news post. It's common for movie news sites to report each others' stories, but they will usually include a link to the source. Click through to the original article, and use it when you post a link on the forums.
You should also think about whether it's appropriate to include a tag in your post. Tagging is discussed in another column, linked here.