Turn off the water supply to the shower
Open the faucet to relieve pressure
Remove the handle screw and take off the handle
Remove the trim plate and any decorative cover
Inspect the valve for the cartridge, stem, or washer type
Shut off water to the whole house if there is no local shutoff
Remove the retaining clip, bonnet nut, or packing nut as needed
Pull out the cartridge or stem assembly
Check O-rings, washers, seals, and the cartridge for wear or damage
Replace damaged parts with matching new parts
Clean mineral buildup from the valve body and parts
Apply plumber’s grease to O-rings and moving parts if appropriate
Reinstall the cartridge or stem in the correct orientation
Reinstall the retaining clip, nut, trim plate, and handle
Turn the water supply back on slowly
Test the faucet for leaks and proper operation
Tighten fittings slightly if leaks remain
Replace the entire cartridge or valve assembly if the leak continues
Call a licensed plumber if the valve body is cracked or corroded