We normally expect film openings to set the entire tone of the film. However, there are dynamic choices which we normally see and expect and there are factors which we do not expect.
In the opening sequence there is normally an establishing shot to signify the time period and location. In some cases, the opening sequence is just of the location and we are not introduced to any characters. However, in most cases the audience sees the victim but the identity of the killer is hidden. This identity is kept hidden by use of tracking shots and point of view shots. In the film opening, there is not immediate action which takes place, but there is a build up and a tension that rises to keep the audience in suspense.
In film openings, we are normally given exposition which sometimes provides the time period/date and the place. On the other hand, this exposition does not always have to be the place or time, but through the dialogue. In the opening, through this dialogue we are introduced to the characters and therefore we can pre-judge. Exposition can also be used to provide anchorage such as in Halloween the words 'Halloween Night'.