Conventions of Film Openings

In most films we are introduced to our central protoganist, or sometimes antagonist, in the opening scene. Generally we are introduced to all central figures one at a time, in order to both build the plot but also simply not overwhelm the audience. In a higher budget films with A-list stars in central roles, that actor/actress is likely to be shown on screen very early on, as they act as huge selling points.
Quite often in opening scenes some kind of substantial event will occur. For example, often an act of violence is shown in horror movies, or it could be simply some action that helps develop characterisation.
Non diagetic sound is often used in similar manner, be it either music or voiceover. They both help to create exposotion to the setting and events, as well as again characterisation.Film directors must attempt to convey many key points in a short length of time in order to draw it's audience in. More sophisticated films do this subtly, and the audience take in key information without realising it. This is what we must attempt to do in our film opening.