Dialogue

In the true spirit of Show not Tell, it lets your readers hear evidence and then judge for themselves what to make of a situation. If you tell us that a character was upset, that’s one thing. But show their reddening face, their clenched fists, and their words—"Get yer sorry [hind end] out o’ my house before I…", well, readers have no more room for doubt.

In formal papers, dialogue (called quotes) can protect you. If you say something controversial, your readers may dislike or judge you (see ethos) and thus make your paper less effective. But if you quote someone else as having said it, you’re safe and you still got your point across.

Five keys are critically important to build effective dialogue:

• Use realistic words. If a typical teen is talking, don’t quote them as saying, "I am going to the store." They almost never say that. It comes out more like, "I’m goin’ to the store," or "I’m gonna go shopping." Use contractions, slang, anything to make it sound realistic.
• Add description. Dialogue is rarely as effective if it’s just the talking. When people talk on movies or in real life, they’re surrounded by many objects and other visual stimuli. All these add context and enrich the meaning. You might describe the way the characters dress, stand, etc. You could describe the setting—is it rich or poor, rugged or refined, comfortable or otherwise? All these details make a difference. Even on radio, you can hear inflection, accents, tone, and pitch, which provide plentiful clues as to the speaker’s identity and feelings. In writing, you must make up for these deficiencies by other means such as adding details and description.
• Add action. This is similar to description, but is important enough to merit its own bullet. This includes characters’ movements, expressions, and other actions. When someone asks how your day has been, does it make a difference whether they’re looking at you or watching TV? Of course it does. If two characters are taking a walk in the canyon, including details (don’t forget sensory details here) can fill out the experience and make it more realistic, which serves to make the words even more powerful.
• You can include internal dialogue as well (thoughts). If you have both external (spoken) and internal dialogue, you can differentiate by using italics for the internal dialogue. Be careful with this one though—it sounds weird if you seem to know thoughts of other characters. It’s usually best to show their actions, expressions, and words that demonstrate their thoughts—the same way that you came to "know" them.
• You can add ideas or themes to anything. This is the least common of these five keys, but can sometimes be used effectively. It’s most common that dialogue is added to passages of abstract themes rather than intentionally adding themes to dialogue.

You'll find good examples of dialogue in most of these essays.