A main “rule” in screenwriting is “show, don’t tell”. A screenplay is emotionally powerful when it engages the reader. When you “tell”, you communicate facts. When you “show”, you invite understanding. “Telling” disconnects the reader from the material, while “showing” connects the reader.
“Show, don’t tell” doesn’t mean you can’t use dialogue to convey information. It means don’t use “on the nose” dialogue.
Your responsibility as a writer is to create scenes to show the reader/viewer that a character is miserable, hates his job, or is in love with someone.
A screenwriter should show specific details that enable the reader/viewer to reach a particular conclusion. Present the dots and allow the reader to connect them.
HOW TO "SHOW" (NOT "TELL"):
Tip1 : Avoid excessive dialogue.
People don’t talk in long soliloquys expressing their emotions directly (“I love you, Tom”). Eliminate all but the most essential dialogue. Don’t use five words when you can use one.
Tip 2: Keep exposition to a minimum.
Real people don’t explain their backstory to strangers or, even worse, reveal information to people that is already clearly known (“As you know, Bob, you’re my brother”).
Tip 3: When possible, convey the information visually.
Film is a visual medium, the more information you can convey with images, the better. For example: The images of the urban city in Se7en "show" without "telling". The reader/viewer can connect the dots and conclude how the characters are psychologically affected by their environment, without the screenwriter having to ‘tell’ the information in a direct manner.