Having complete darkness with only a glimpse of light and a innocent person standing makes the audience feel scared as they wonder what could be in that big patch of darkness.
Sometimes when an image of a person looks blurred or confusing it makes the shot look more spooky as the audience can no identify what this human actually looks like it creates mystery and a urge to know more.
In some film shots the audience are aware of the the troubles that lay behind them but the character playing the victim does not. So when a scary child appears behind them admittedly we want the person to turn round and see what we see but they wont because they are facing the camera.
Having a close up of a scary faces with darkness surrounding them identify's what the villain looks likes and may give a fright as it appeared out of the darkness.
Shots that just show a shadow of a figure makes the shot scary as we can actually identify who it is , it keeps the audience wanting to know more.
This is a picture taken from the film 'The Shinning' and this is an iconic seen for most people who watched this film. As just by seeing the expression in his face we can tell that he is psychotic.
Close ups are also good because it builds up tension for example in Se7en we only see close ups of his fingers and objects he is using - it makes the audience feel uncomfortable.