Use a damp cloth or soft bristles to clean inside the grooves, which put spin on the ball.
Plastic covers that slip over each iron can prevent scratching.
Wash the clubheads on a regular basis, using soap and water or a damp cloth. Use a damp cloth to wipe down each grip and shaft. Store your irons in a dry area after each use. Avoid keeping them in the trunk of your car or in your garage. These areas are subject to temperature changes that can damage grips and even shafts.