To add news, edit Template:News.
Add new news at the top.
If there is too much news in the news box (meaning that the height of the news box on the Main Page is more than 1.5 times the height of the 'main content' column, then delete old news from the bottom.
Start each news item with a *.
Don't overdo it; don't claim the whole news box on the Main Page for your own projects.
News headlines in the news box should have links to news pages or other pages, or sections thereof.
link to page: [[page]] link to section: [[page#section]]
News pages should have clear and unambiguous, and preferably also systematic page names / titles. Ideally, some kind of newspaperish name plus date, for example:
Plutonian Times of July 2012
Alternatively, if you expect news from a certain project to be infrequent, you can just make a single news page '
News from Pylaria' and add new section with new news at that page. (And link to those new sections from the headlines in the news box.) In that case, it is probably best to add new news sections at the top of that page (rather than at the bottom).