Paint your walls a light blue or other soft, light color that will brighten the appearance of the couch when you add corresponding pillows that pick up the wall colors.
Contrast the sofa with a lighter colored companions. Make sure the wood of the legs on a chair or the trim of an ottoman or loveseat match the color of your leather couch.
Use throws in large patterns to break up the solid feel of the furniture or throws in silks or cashmere to soften the leather's appearance.
Use light, breezy curtains that let in plenty of light and have a see-through look. Use sheepskin, alpaca or flokati area rugs to add thick textures that offset the sparseness of leather.