One of the first things people notice about bad storytelling is its "obviousness," and this video essay from Film In The Making examines a few scenes from famous films to show how dialogue can be used to convey more meaning than just surface level expository information, and subtly foreshadow plot points or reveal hidden character traits.
In the opening scene of Reservoir Dogs, for example, the characters sit around a table in a diner having a conversation that is the quintessence of Tarantino's style: cool, funny, and obsessed with pop-culture ephemera. The scene, however, communicates more than just mood; important story information is hidden in the casual conversation, which also serves to introduce the characters. At the end of the meal, Steve Buscemi's character, Mr. Pink, puts forward his rationale against tipping. When Mr. Cabot (Lawrence Tierney) returns to the table, counts the money, and demands to know who hasn't chipped in, Mr. Orange gives up Mr. Pink.
Later on, of course (SPOILER ALERT), it's revealed that Mr. Orange (Tim Roth) is an undercover cop, and that Mr. Pink will, given the chance, flee with the diamonds. From the first scene, Tarantino is encoding important information in a subtle way. Skillful foreshadowing should go unnoticed on first viewing, absorbed by the audience on a subconscious level. Tarantino's characters, and their back and forth, may be cool, but the director also "implicitly reveals character through dialogue," which is accomplished by setting up a reason for Pink's dislike of Orange, and therefore part of his motive for accusing him of being a rat. However, this is also a trick, because while the audience, desirous of cause and effect, attributes the dislike to personal reasons, Pink is in fact correct about Orange; the answer is hidden in plain sight.
Video is no longer available: www.youtube.com/watch?v=IlXwTxpC6u0&ab_channel=shark15
Another example of dialogue setting up the story without explicitly telling the audience is found in The Social Network. Master of dialogue Aaron Sorkin turns tech mogul Mark Zuckerberg into a villainous misanthrope, whose success comes at the expense of human warmth. He goes through the film "offending people and getting sued," and the only time he ever apologizes is during a breakup in the first scene. According to the essayist, the apology is "awkward and robotic," and foreshadows Zuckerberg's character arc. The very thing that will make him successful, his deception and inability to relate to other people, is what generates the pathos in his character and makes him the tragic figure known in Greek tragedy as "hamartia".
"The dialogue that we use in day-to-day life isn't usually suitable in a film."
As Film In The Making's James Hayes puts it, "the dialogue that we use in day-to-day life isn't usually suitable in a film," but that's the beauty of dialogue. Artfully deployed, it gives the illusion of life, and is, in some ways, truer to life than life itself. If you can make your film's dialogue more than just words the characters say, but turn it, instead, into a covert exploration of their wishes, fears, and schemes, you'll enrich your story and, just maybe, weave the words of a simple conversation into dramatic gold.