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)