Ok, so what is the 180 degree rule again? It's a rule of composition. So say you have Mr A and Mr B facing each other in a video shoot. They're talking to each other intensely. Your camera must be on the right of Mr A and left of Mr B, as shown below.
 

The 180 degree rule in digital videography
 

Imagine if both Mr A and Mr B were facing your camera instead. What would you, as a viewer, think? You'd think they are talking to the viewer! So that is the essence of the 180 degree rule. Keep your camera on the "sides" of the subjects if they are engaging or speaking to each other.

The 180 degree rule certainly doesn't apply in all situations. If you're filming two people talking to each other, then yes, it is useful to apply it. You should not apply this rule if you're shooting a basketball game or action in sports, for example. That just would not make sense. I find that I usually apply to situations where you have 2 subjects engaged in conversation.

You can also very cleverly use the 180 degree rule to intentionally trick or confuse the viewer. Let me explain. Imagine Mr A walking along the street from the left to the right of the screen. Next, imagine Mr B walking along the street from the right to the left. Our minds would naturally think that Mr A and Mr B are walking towards each other.

Now imagine you cut the scene of Mr A out to its surroundings - maybe it's in some urban business district. And cut the scene of Mr B out to say, the Sydney Opera House. Now you know that Mr A and Mr B are in totally different places. If it was your intention to conceive such a scene, the 180 degree rule helps you out, as you can see.

Sometimes, it can be boring just having your camera on the 180 degree plane showing the 2 subjects. If the video camera has been rolling for 15 minutes and you've not moved your position, your video might start getting boring.

What you can do in this case, to liven up the video, is to use a neutral shot. Get a close up of one of the subjects and make sure he or she is not directly facing the camera (example below).
 

How to use a neutral shot
 

This helps cut away the monotony of the shot and bring more life to the video. You can then cut back to the original shot which follows the 180 degree rule after concentrating the close up of that one subject.

The 180 degree is an interesting concept in videography and it is used sometimes without us even realizing it. But I guess it's always good to know there are such rules out there. If you want to find out about formal video editing rules,