Writers and editors conform to a common style for the sake of consistency and to rule out poor practices. While these guidelines may be established by the News Director, often they are derived from one of the well-accepted style guides.
Many ND’s simply go with Associated Press (AP) Style. You can now find the AP Stylebook online, which allows quick searches and allows you to save your own variations. The AP has different guidelines for broadcast and print or online.
A well-respected style guide for broadcast and online news is provided by The BBC.