Hereditary acts clever by leaving hints to later events scattered throughout this movie. But unless this is your first "horror" film I doubt anything that happens will be too surprising let alone scary. The characters themselves are insufferable to the point where seeing them be tormented is a welcome relief. I have seen and read other reviews that people have written stating that this film stands as a sort of role model to future horrors this is true in the way that criminals are good role models to small children.
If I could give any advice to people that are thinking of watching this feature length atrocity skip about the first hour and 20-30 minutes and watch it as a short movie.