The Motion Picture Producers and Distributors Association's (MPPDA) "Don’ts and Be Carefuls" of 1927, a forerunner of the Production Code (1930) and the Production Code Administration (1934)
First feature: Becky Sharp (1935), see low-res YouTube version:
Various three-color Technicolor samples:
The Continuity Editing System
The 180 Degree Rule Axis of action and shot-counter shot (aka, shot-reverse shot) Source: David Bordwell and Kristin Thompson, Film Art, 9th ed. (NY: McGraw-Hill, 2010), 237.