Previously published Wikinews articles can (usually) be used, cited in a separate section.
You still need two independent external sources for the news event of your article.
As long as the other article is reasonably modern (2009 or later),
and you cite the other article properly,
you'll be able to copy text verbatim from it, without violating copyright.
You should first learn the basics of Wikinews writing.
Although there is some basic information about OR below, before actually trying it read Wikinews:Original reporting.
Simple original reporting can add extra value to a basic article.
At the most advanced, interviews may be pure original reporting with only a bit of background from external sources.
Detailed reporter's notes must be provided on the article talk page. The reporter's notes must verify everything in the article and pinpoint where all information came from. Include everything you can, like transcripts of phone conversations, emails, etc.
Be especially careful to maintain neutrality and avoid conflict of interest when doing original reporting. If you go to a protest to participate in it, you can't also be a reporter covering it (though another, neutral Wikinewsie might conceivably interview you).