I usually fit them about 6" above the tub.
About 26 inches above the floor if it's only a bath faucet. 30 inches if it is a shower control too.
When installing a bathtub faucet or tub & shower divertor valve, the bathtub spout must terminate above the flood level rim of the bathtub a minimum of 2"inches.This would place the stub out for the spout approximately 6"inches above the rim of the bathtub.Now just install the faucet or divertor high enough so the trim plate will not contact the spout.12 to 15"inches above the spout should be fine.
The spout opening on the faucet must be at least 1" above the flood rim of the sink which would be the top of the counter.
Provided they are at least a metre above the height of any bath and not directly above it, and unreachable when in the shower, they should be safe.
48" for a shower and 15" above the tub for a tub.
I design hotels for a living and all showerheads in new hotels are installed at 6'-8" above finish floor. That is the location of the connection at the wall. The shower head pipe will have a bend in it that usually puts the head itself and around 6'-4"
I generally mount them so the spout is about 3 inches above the sink, but a lot depends on the design of faucet.
above it in the wall
I always tile to 72 inches above the shower floor.
According to Building Control Regulations, the DPC should be a minimum of 150mm above external finished ground level.
You can put it at any height. Unless there is some other reason not to, something structural, I always put them above the shower stall for taller people.