180 rule

 

The 180 degree rule is a rule of thumb which says that if your filming an interaction between characters, cameras should be placed along one half circle of the characters. By doing this, the placement of characters within a scene is clearer to an audience. Similar to the 30 degree rule, this makes it easier to effectively cut a film. Additionally, this is an easy way to use cinematic language to convey the difference between two characters. 

(I would argue that the way the characters are looking within the set is more important, however when working with less trained actors the 180 rule is easier to follow).