The Voiceover

One of the main conventions of a film trailer is the voice over. This can be performed either by a narrator or by one of the film characters. The voice over has many functions such as :

• Helping the audience to make sense of the narrative by giving background information such as the setting of the film or character introduction.  
• They introduce the stars of the film as they appear on screen.
• Gives information about other important personnel such as the director, and gives examples of well known previous works.
• Sets the tone of the film by using an up-beat voice for a comedy film or a deep voice for an action film etc. 
• Summaries the story in around 5-8 lines re-enforcing the action on the screen without spoiling the film. This helps to build tension and make the film more appealing.

The voice over is arguably one of the most important parts of the trailer, creating tension as the music and story of the trailer progresses. The voice over in horror films is usually voiced by one of the protagonists of the film, with clips of dialogue taken from the film and ordered to give a back story or introduce characters during the trailer. Another convention in horror film trailers is to have the voice over reading a poem or something to do with the plot, in order to create tension, but a direct voice over where the narrator talks about the actors of the film is not normally used in a horror film trailer.
This is a good technique, and I am planning to have a narrator reading a poem on my trailer as I feel that this would be a great way to create tension, as well as connote my plot to the audience.