Wet a piece of medium-grit sandpaper and run it over the entire surface of your leather sofa. Press gently, and pay special attention to areas where dirt and grime has accumulated. Wipe off the surface with a clean, dry cloth after sanding.
Repair any cracks in the sofa with crack filler that matches the color of the sofa. Follow manufacturer's instructions for filling cracks. Repair stains on the sofa with a leather cleaner. Use a soft-bristle brush to scrub the stains until they are lifted from the sofa.
Rinse the bristle brush thoroughly. Follow manufacturer's instructions for dye preparation. In a circular motion, rub in the dye with the soft bristle brush. Use two coats if necessary to restore leather to its original color. Allow dye to dry for 48 hours before using the sofa.
Use a soft cloth to apply leather polish. Rub polish thoroughly in a circular motion. Continue to rub in polish until the sofa returns to its original luster.