The 180* Rule

One of the most basic continuity rules is the 180 Degree Rule.

The 180 Degree Rule states that two characters in a scene should always have the same left/right relationship to each other. If you don't follow the 180 Degree Rule, or break it intentionally, it disrupts the scene disorients the audience. When you break the 180 line, a person who was originally facing left in a scene is all of the sudden facing right.

Here is an example of the 180* rule