Although specifically Psychological Horror codes and conventions were covered earlier I have however not covered basic horror codes and conventions in general. The following is a list of general horror codes and conventions although not always strictly followed they are a guidline for most horror films.
Male Protagonist: Nearly always in a horror movie the Protagonist (killer) is a male, this is probably because in society in general; although not so much now, people used to associate murder with a male killer because of their dominance and power/strength, this is also likely to be the case since most murders are still committed by men.
Victims usually have an attachment to something when they are scared: For example victims usually go to friends or family in times of trouble or perhaps turn to religion and even the police, horror films operate by depriving the victims of these things perhaps by the protagonist killing family members or friends etc.
Equilibrium disrupted: Horror films usually start off normal, like maybe any other drama/soap opera, but then this equlibrium is disrupted (disrupted normality). Something in the film has to then happen to create a new Equilibrium (normality) usually different than how it was before.
Female Victim: Traditionaly in older horror films such as Psycho (1960) the victim is a female, this film helped to reconceive how audiences see horror i.e. not just monsters that are scary but also humans. This convention is however not as common anymore although still used in many films in the slasher genre.
Romantic Sub plot: Probably more than any other film in which romance (excluding the romantic genre itself) is present is in the horror genre.
Antagonist (main character) kills the Protagonist (killer): Relating to Equilibrium often the Antagonist creates a new normality by killing the Protagonist. They are usually strong, intelligent and determined, in the Slasher genre they are usually female.
Isolated setting: The use of an isolated setting increases the distress and fear that the characters suffer- know-where to run and hide.
Dark setting: The setting of horror films is very often set during the dark at night. When people are at their weakest and cannot see as well, also fewer people are around to help.