First and foremost, don not write camera angles into a script for a three- or four-camera show that is shot in front of a studio audience. Shows that use this setup are usually sitcoms, and there is no need to specify angles since several cameras are shooting at several angles all at once. If there needs to be a particular insert shot (e.g., a ring on someone's finger) that can be called out as: INSERT: CU ON RING ON FINGER (CU meaning closeup).
For a one-camera show where a more traditional script style is used, you can call out special camera angles to highlight elements of your script that you feel need to be made a focus. For instance: ANGLE DOWN SLOWLY CU OF BRAD'S SHOES. In this way you can present the idea that looking at the way Brad is dressed compared to his shoes makes an important statement about what is happening onscreen.
You can also call out shots that need to be shot a certain way for storytelling reasons. For instance: CAMERA SWINGS AROUND WILDLY. This means no one is in focus, arms and legs are kicking and hitting any flesh they can find. The fight is on. The main thing is not to use these types of camera suggestions too often. They must help move the story forward and, most importantly, they need to be discreet and important shots that require the writer's input to effectively tell the story.
Every writer loves the control of writing in such a way that a story just comes to life in a reader's head. It's the same way for TV scripts: Write what needs to be seen. Don't worry about adding unnecessary camera angles to a script that doesn't need them; it can sometimes upset the director, who, naturally, wants control over the camera. But when used selectively, they can make production go smoother and make your script a better read.