Horror Genre Conventions

Settings:
Small communities or isolated places, normally abandoned or have very few people living there. Gives a sense of being isolated from the rest of the world.
Often places with a 'past' which will return for example old abandoned houses, or old asylums like the one in Grave Encounters. Normally places with multiple levels basements and attics etc.
Night time, sometimes a nice place during the day but then becomes different at night.
Religions/medical institutions - possession, demons etc. Can also take place in dreams or the unconscious mind (Incidious).

Technical Code:
Camerawork is expressive rather than naturalistic, high and low angles and canted camerawork is also common in many horror films.
Extreme close ups on victims lets the audience into the victims person space and they get to experience the horror that they are feeling at that exact moment. Sudden ECU's are also used on the monster/villain to show an invasion of personal space.
Point of view shooting is very important, hand held cameras etc. Camera often places audience in monsters eyes like at the opening of Halloween.
Camerawork often makes use of depth of the frame - protagonist in foreground unaware or monster in the background.
During the editing process you can create unsettling jumps from long shots to close ups rather than doing is smoothly by zooming in or going to a medium shot. You can also change the pace of the shots which can also have a huge effect on the film and its audience.
Sound is sometimes very important, ambient sound for atmosphere, footsteps, heartbeats high in the sound mix.

Iconography:
Visual signifiers - Black and red - blood, darkness and evil
Lighting expressive but not natural, motivated, low key, high contrast, chiaroscuro, emphasis on shadows. lighting direction often from unexpected  angles eg below a persons face to create weird shadows. Sunlight, moonlight, room lights always from above.
Commoner objects in the mise-en-scene would be things like weapons of the iconic knife, blood, masks, ghosts and moving objects etc, also things to do with religion and cults
Children are normally associated with innocence - dolls and playgrounds even clowns also children's songs are used in horror films to give the audience a sense of false security, they think the child is innocent with dolls and the songs playing in the background, where actually they are the main monster like in The Ring

Narrative Structure:


Character Types:
Main protagonist often the hero or victim.
Monsters with hidden secret or troubled past
Stupid.immoral teens get killed
Children
Ineffectual police and normal law enforcers (horror is not containable through normal channels)
The have a go hero who will get killed
Scientists who do stupid things or over reach their powers (Frankenstein)
People who refuse to believe

Themes:
Binary oppositions - Natural VS unnatural, good VS evil etc
Return of the repressed, Freudian theory, horror is often close to sex in some way.
The hidden evil inside
Science out of control
What lies on the other side of death