A reserved character may still betray some emotion through action, dialogue, and appearance. The details, however, will simply reflect her more restrained personality. When she’s angry at dinner, she might not sweep the dishes off the table and storm out, but she might pick at the napkin in her lap, or bite the inside of her cheek. Find a detail that captures her unique experience of the emotion.

You might also use your characters inner experience to more fully develop her character. Annie Proulx’s short story “The Mud Below,” features Diamond Felts, an accomplished bull rider. In some ways, he’s a restrained guy. The first time he rides a bull, there’s little outward detail to indicate his intrigue. When invited to try it he says, “Yeah, I guess I’ll give it a go.” But Proulx reveals the power of this experience by turning our attention to his internal world:

But Diamond stayed on until someone counting eight hit the rail with the length of pipe to signal time. He flew off, landed on his feet, stumbling headlong but not falling in a run for the rails. He hauled himself up, panting from the exertion and the intense nervy rush. He’d been shot out of the cannon. The shock of the violent motion, the lightening shifts of balance, the feeling of power as though he were the bull and not the rider, even the fright, fulfilled some greedy physical hunger in him he hadn’t known was there. The experience had been exhilarating and unbearably personal.

Diamond experiences something significant here and this gives a glimpse into the nuance and nature of that. There’s not a lot of carrying on about it, but there’s enough to show the reader the intensity of that experience for Diamond.

You can also use language choices to reveal more of your character’s experience. In Aleksandar Hemon’s short story “Blind Jozef Pronek,” Jozef leaves Sarajevo for the United States as tensions rise in Bosnia. In Chicago, he catches glimpses of the devastation of war unfolding in Bosnia as he navigates his day-to-day life. His outward emotions are mostly restrained, but his thoughts are often on his family’s safety and the violence that is taking place in Sarajevo. At Boudin Bakery, where he finds a job, descriptions are haunted by the language and imagery of the atrocities of war:

By the end of the first week, Pronek was in charge of garbage disposal. He emptied abandoned trays with hollowed-out loaves, mauled croissants, and desiccated bowls, and then pulled out the loaded garbage bags and dragged them off, like corpses, to a nook in the kitchen.

The same tools and techniques are available for the restrained character as for any other character. It’s a matter of how you use them to fully articulate the unique nature of your character.