Turn off the water supply to the shower
Remove the handle screw or cap
Pull off the shower handle
Remove the escutcheon plate if needed
Inspect the cartridge, stem, and O-rings
Replace worn O-rings, washers, or cartridge parts
Apply plumber’s grease to moving parts
Reinstall the handle and tighten the screw
Turn the water back on
Test for leaks and tighten or replace parts if needed