A dripping shower head usually results from worn washers or O-rings inside the valve. Turn off the water supply remove the handle and access the cartridge or valve stem. Replace worn rubber seals and reassemble. If the cartridge itself is damaged replace it entirely. For compression faucets replace the seat washer. Apply plumber grease to new seals for a proper fit. Mineral buildup can also cause drips so soak the shower head in vinegar overnight.