Dampen a soft cloth with warm water and a drop or two of dish soap.
Squeeze out the cloth and wipe the front of the couch. Start from the top and work your way down. Make sure to clean the arm rests and cushion fronts.
Use a clean, wet cloth to remove any soap from the leather couch. Rinse the cloth periodically to ensure you're not leaving any residue behind.
Dry the couch quickly with a towel. Make sure to get down into any cracks or between the cushions where water can pool.