Television is a visual medium, so the visual elements are important. Shade the cameras properly, white balance, make sure the talent is in the right spot for optimum lighting... pray Overdrive or Ignite don't do anything weird.

Input one incorrect piece of code and the camera leaps out the window.
We could run in circles discussing content. Viewers tell you they hate crime stories, yet the station leading a newscast with eight consecutive crime stories wins the time slot. Go figure. :

In a market with millions of potential viewers, it is impossible to please everyone at once. This week we did two stories in one suburb about a substation built much, much larger than planned, and planned without alerting some of the neighbors. It's an important issue to this suburb, but probably not to anyone on the opposite side of the market.
Perspective is vital. Don't just tell the facts, but why it matters. Storytelling is important. If you don't capture a viewer's attention in the first sentence, they're probably gone.
Weather, at least in our market, is among the top interests of potential viewers. Viewers want to know the weather for tomorrow, and the weather for the upcoming weekend. In an hour-long newscast, that is also why meteorologists wait until the last weather segment (xx:45) to reveal the long range forecast. Sometimes a sound effect accompanies the long range forecast to grab any distracted viewers. They're trying to maximize viewership for that hour. If it rains, my competition will make weather the lead story, which irritates me. But it works.
Newscasts are longer, and there are more of them. We try our best to generate original content for each one, even though we have fewer employees than four years ago. To keep a viewer interested for a full hour, teases are necessary. When I produced 9:00 p.m. shows, I treated each block like a miniature newscast. But a top story is a top story. No station would wait 45 minutes to tell you every loaf of bread in the city is contaminated with strychnine.
Those ten-second teases you see during prime time are called topicals. Don't ask the viewer a question he or she can't answer (i.e., will it rain tomorrow?). Considering the brief time allocated, stations need a talented writer to avoid looking foolish during those teases.
Lead-ins are important. Ask NBC affiliates. Know your lead-in audience. Learn whether it is mostly male or mostly female and consider your stories armed with that information.
Sadly, though, I've learned viewer habits are hard to change. The market leader has been the market leader since the early 1990s. People who watched that station pass those habits to their kids. I could lead my newscast with a story about the Governor personally murdering his political enemies on the statehouse floor; the market leader could put a watermelon on the set and do nothing... and more people would watch the watermelon.