How can you tell a movie is good or bad from the writing?

Whenever you read reviews or just hear people talk about movies, they would often used certain buzzwords to describe how great or terrible a movie can be. For example, “I found the movie terrible because it has ‘bad writing’ and ‘bad directing’” or “great because of the good writing and directing”. I really don’t get how people could sense a bad script right away from watching a movie sometimes, unless they also happen to have a script sitting right next to them as they watch the movie.

May be there are times where I could sense some awkward dialogues coming from the actors as a part of the indication for ‘bad script writing’ on the writers end, even when the story a movie had to work with is weak too, but how could the Average Joe always sense those things from just watching a movie (or show)? The same thing when it comes to good or bad directing.