A news bulletin is an essential part of the radio schedule and listeners expect to hear a good mix of stories – some serious, some light. They also expect a certain pace. A report of a fire for example, will usually be short and snappy using simple words to convey the message; by contrast, a story explaining some complex political controversy will take longer to explain the issues and therefore have a slower pace.
The actual order of a news bulletin will depend to some extent on the station format; serious national broadcasters will use more serious stories, delivered in a more deliberate style, whereas youth-oriented music stations might prefer lighter and brighter stories about popular culture. However, the basic principles are universal and if you apply them carefully you can build a bulletin which is well balanced, well constructed and, above all, interesting for your audience.
You should try to stick to current events, reducing the delay between what is happening and your audience hearing about it. A good rule of thumb is to spend about 2 minutes on your main headline story.
You should always re-read the entire bulletin before it is broadcast to check that all the information is correct and that the tempo of the reading is appropriate. It is also a good idea to time each item; if you have practiced regularly, you should be able to look at a piece of text and estimate within a second how long it will take to read.