The 180 and 30 Degree Rule

The 180 Degree Rule.

The 180 Degree Rule means that two characters in a scene should always have the same left/right relationship to each other. When you break the 180 Degree Rule (also known as crossing the invisible line and it sometimes done intentionally), it disrupts the scene as well as confuses the audience. The camera needs to be kept on one side of the environment you are in. 

A video explaining the 180 degree rule.

The 30 Degree Rule.

The 30 Degree Rule is used to create continuity. When you're moving the camera between shots, it should be moved in a minimum of 25-30 Degrees to avoid jump cuts (also known as Jarring Transitions). For example if you want to show a facial expression on a certain character but you are currently filming in a Wide shot then you would use the 30 Degree Rules and move into a Medium or Close up shot so it doesn't seem like the camera has just jumped and cut forward.

A picture showing the camera moving 30 Degrees.