How to add voice to your writing

Choose a "hot spot" in your scene, such as between two actions by your character.

Open up a new document and spend some time free writing about the characters' emotional landscape at that moment in time. Don't worry about punctuation or sense or anything, just write down everything that your character could be thinking and feeling at that point.

Go have a cup of tea. Leave the writing alone for half an hour.

When you come back to it, pick a few sentences from your free writing to add to the manuscript at that point. Not everything will be gold, but it doesn't matter.

Pick two or three places in each scene to do this to add style and characterisation to the chapter.

Example from the text:

The hot spot is like this: “There’s no easy way to put this,” Dirk said. “It’s Hank, isn’t it?” Dirk nodded. Jen put her hand on her mouth. Closed her eyes. A pitiful whimper sounded in her throat. Dirk said, “You need to sit down.” “Don’t tell me that!” Jen turned and ran upstairs. A door slammed. Dirk thought for a moment about going after her. But he decided to let it go. She needed time to be alone. He took a sip of coffee. It was bitter and lukewarm. Then he put the cup down and left through the front door.

Yeah, bitter and lukewarm, like my damn life, like it’s always been, and Pop told me that’s what I was, lukewarm and a coward, afraid to face anybody or anything, so when I left home for the first time at sixteen I made sure I screamed in his face How’s this for lukewarm! How’s this, Pop! I’m getting out for good! and all he could do was stare at me like I wasn’t even his son, like I was an alien or something, and here I am in the middle of this thing, this killing, and my damn soul is as cool as that damn coffee, because I don’t really care, I closed off caring, remember when you did that, pal, you were in San Antonio that time, that one time you found somebody who really cared about you, loved you in fact, that’s what she said, and you used her for a week then walked out on her and never looked back, so why don’t you for once follow up on something and go up there and tell this woman you’re not going to walk out on this, you’re going to find out who killed Hank, and if you do maybe you’ll connect with a person like a real human being is supposed to.

Source: How to Write Pulp Fiction - James Scott Bell