Will the movie you're starting to watch be any good?

Does it start with the protagonist brushing their teeth? => It probably won't be any good. This is typically the work of a weak director who is using a cliché to portray aspects of a character early in a film (how they get ready for the day can reveal a lot). It is often typical of romantic comedy films that you don't need to finish watching.

Does it start with a shot of a city-scape? => It probably won't be any good. This is also an amateur directorial technique used to establish setting and mood (usually by the weather and time-of-day of the shot). It's okay to show a shot of San Francisco when watching Full House, but otherwise it's generally a waste of film.

Exceptions to these rules: Stranger Than Fiction starts off with the main character brushing his teeth, but it's for a reason. Blade starts off with panning over a city from the top (not a typical landscape shot of a city), and it's sunset scenery is used to convey the transition of the city into the world of the vampires.