Making smart choices right in the beginning of the movie.
Majority of horror movies have a similar plot: Buying a haunted house.
The protagonist and his family is looking for a new house to settle in and ultimately they found one which is always a huge mansion.
Before they buy it the property dealer gives them a history of the house and the previous owners who have died under mysterious circumstances and whoever brought it dies in similar manner.
What do the protagonist do: use his common sense and leave or buy it because its extremely cheap?
They always choose to buy it ignoring the warning. Making dumb decisions in the start of the movie. In the end as always they beat whoever is haunting the house and live happily ever after.
Confirm the kill.
Making sure they actually killed the demon/zombie who is haunting them.
Most of the time they shoot it once, only for it to appear again later.
Investigating the noise heard from the basement or room which the property dealer specifically told not to open.
Worst part is they usually check out the noise at night all alone and unarmed.
Going down the basement, all alone, usually when ball or something falls down.
Running at the last moment when the ghost is near. Start running at the first instance when you find something is wrong.
Tripping over literally nothing when the killer chases and looking back again and again until they stumble over something.
Running upstairs when the killer chases. Never run upstairs to get away from the killer who's in the house.
Hiding secrets that gets everyone around you killed and only reveals the truth when the entity goes after your partner or children.