Preassemble the shower valve by soldering copper nipples and the shower supply pipe to male adapters and screwing them into the shower valve before fastening the valve to the blocking. That way you won’t damage the valve with heat from the soldering torch. Mount the valve 36 in. above the floor. You can mount the showerhead at any height, but plumbers typically mount them 6 ft. 6 in. above the floor.
Turn off the main water supply to the house, and in a convenient location, cut the hot and cold water supply pipes for the bathroom. Also cut out and remove all the existing water lines and fittings in the bathroom. Finally, cut out and remove the vent section leading to the sink and the main stack 5 in. below the vent tee. Stuff rags into open drain lines to keep sewer gas out of the house.