What is needed to give you a strong narrative of a film?

To have a strong narrative for a film there are key elements that need to be shown in a trailer in order for the audience watching the trailer to get the general idea of what they films is about with out giving away to much information.

Some key points that are needed are

• Glimpse of who the main characters are
• voice over or writing on the screen ( allows the viewers to have a bit more information about what is happening) 
• main event snippets
• a shot of the location   
• a shot or mention of the bad thing (the killer, ghost, demon, vampire) 
• music to give you the feeling that it is a horror
• the makers or producers of the film ( some production companies such as twisted films are known for horrors)