Fixing a shower faucet leak usually involves replacing a worn O-ring. The O-ring is a small rubber ring which seals the different parts of a shower together at the joints. We have a number of O-rings in different sizes. Most showers are uniform. It is a good idea to remove the old O-ring first. Bring it with you to ensure you find the right replacement. 

A Simple Repair

Remove the worn O-ring in 3 simple steps. First, remove the handle and escutcheon to expose the shower valve. The escutcheon is the plate behind the handle. There is one valve in the center, the control valve. There is a valve on either side of the control valve for hot and cold water. Second, shut both of these off with a screwdriver. You should now be able to remove the control valve cartridge. Take this part with you, and fit it for a replacement O-ring. Fixing a shower faucet may involve replacing the cartridge in some rare cases.

-As a side note, some faucet brands carry lifetime warranties, so check with your manufacturer, first.