It might seem as if anchors don't have much to do but read from a prompter and look nice, but, there's a lot more that goes into anchoring than that. My first producer explained live news like this, "There is a train that's coming at 6:00. You have to get on that train, prepared. If you're not ready, the train is still leaving, and you will still be on it."
When I worked night-side, as a local news reporter and anchor, my shift started at 2 p.m. I would have already read the newspapers that morning, so I knew of any big stories, local or world.
2:00 - As soon as I arrived at work, I'd immediately go to a staff meeting with the News Director. All producers, assignment editors and on-air people attend. We discuss what's happened since the morning broadcasts, any stories we're researching or any packages (series or long-form news format) we're working on. The News Director assigns everyone a story for the next broadcast and we get to work.
2:15- I would usually have to make phone calls to arrange interviews. Hopefully I found someone to give me a comment on tape fast and arranged a meeting with them. Sometimes I could be on the phone forever, or would have to go out and get a general statement from a random person, a MOS or, Man On the Street interview.
2:30 - If I was lucky, I was assigned a photographer to help me shoot the story and my stand ups (when the reporter is on camera talking in a story.). Sometimes, I was a "one man band," which meant I did interviews while running the camera, shooting all the video by myself.
4:00 - Once my story was shot, I could write my story, usually in the van on the way back to the station. I'd record my voice overs (me talking on top of video) in the sound booth and race with the recording to an edit bay to edit it all together.
5:00 - Now, if I was a reporter, you'd think I'd just turn in the tape and relax, but, sometimes, I had to go back to a scene of a story, or a place representing the story for a live shot. For example, if I am doing a story about drug use and have an interview with a doctor in the story, I might be standing in front of a hospital. I would present the story (package) and conclude after it runs. Usually the anchor will ask a couple of questions, which I've written out for them ahead of time. The whole thing can take an hour to set up and airs for just 2-3 minutes. Did I mention I have to look good?
5:45 - If I am the anchor, which is the focus of your question, I already have an idea of what the newscast includes. Stories can always be added, even in the middle of the broadcast. I will, again hopefully, have the rundown of the show and any scripts. I need to put on make up and fix my hair (I got more complaints about my clothes and hair than anything I ever said on-air.) I try to read through the scripts and make sure I know how to pronounce any unusual names. When Christopher Reeve died, I wasn't sure if it was Reeve or Reeves. Good thing I checked.
5:50 - I go to the studio and put on my mic and IFB, which is the thing you sometimes see in our ears, like an FBI agent. I do my sound checks and make sure I can hear my director and producer.
5:55 - Then, if there is time, I check out the shot sheet on my script. This is a column that tells me which camera I will look at for each story. Sometimes there is time to run through the top stories on the prompter. Usually I just practice a few from my script to prepare.
6:00 - We go live. The train leaves and, hopefully our team hasn't missed anything. Interns, producers and photographers are watching our competition on t.v.s in the newsroom to see what the competition is doing. We wrap at 6:30.
The next show is at 11:00. The train is coming again!