Here are cinematic examples of everything I know about dialogue, basic to advanced. Listen…
Buffy the Vampire Slayer. The intersection of your normal world and your story world. Immerse yourself in your character’s point of view… and just tell the truth:
Gilmore Girls. Adversarial dialogue. Watch for the set-up… and the payoff:
Firefly. There’s jargon… and then there’s language. Do you have the guts to try this?
The Avengers. Adversarial, metaphorical, agrammatical, great use of beats:
Bonus Avengers, for the art of the POV monologue, and the importance of character names for each other:
Heist. Now that you get Joss Whedon, you are ready for David Mamet. Once you have the skills to make your dialogue sound totally natural, you can dare to make it sound unnatural:
Brick. Dialogue so good, they printed it in the trailer. If you can write this, there’s nothing more anyone can teach you: