Let’s start with dialogue first. If we’re talking about realistic, contemporary characters, the thing to keep in mind is that if you listen to people talk, we tend to be lazy in our speech. We cut corners whenever possible. We use a lot of contractions. When I come across dialogue where all of the words are written out, it always throws me from the story, thinking, “People don’t talk like that.”
For example: “I do not know where Martha is. She has been gone all day.”
In real life, it would sound more like: “I don’t know where Martha is. She’s been gone all day.” You could even change “don’t know” to “dunno” to show if that character is particularly lazy/comfortable/casual.
Every character is different. Perhaps you are writing a stuffy college professor who speaks eloquently and would never be lackadaisical in their speech. In that case, perhaps no contractions. Bigger words/vocabulary. As the author, you know your characters best. Dialogue is an amazing way for you to show us the characters’ backgrounds and personalities. Do they cuss? Do they stutter? Do they excitedly shout, or speak in a timid whisper? Are they serious or funny? Sarcastic or sensitive? The possibilities of what you can show about characters through their dialogue is endless.
One of the things I often see while critiquing is a string of dialogue with no action thrown in. By “action,” I don’t mean anything crazy. I’m talking about the small nuances. When we read line after line of dialogue, we start to imagine the characters standing there, arms at their sides, unmoving. It’s a delicate balance of action and speaking that takes place, weaving together to create a scene. Even two people talking can create a scene with tension or comfort—whatever your target feeling is.
When you’re writing dialogue, try to imagine what the characters are thinking, feeling, and doing. Are they looking at each other? Is one of them picking at their nails? Is one of them staring at the wall with their arms crossed? Pacing? Moving closer/farther? Is one of them blushing? And what about their tones? Use dialogue tags (he said, she asked, he begged, she whispered) to show the reader what the character might be feeling in that moment.