prudent pre-shower protective procedures

Preliminary actions that you should always perform prior to partaking of a sudsy scrub--a-dub, to avoid any "unintentional ice-bucket challenge" surprises that often occur while you're waiting for warmed aych-two-oh to flow from the water-heater through your pipes to the shower-head.

These two prudent pre-shower protective procedures are very important to avoid potential bathtub-hypothermia, but are very simple and easy to carry out:
(1) Ensure that the tub/shower selector-knob is moved to :"tub" so that water will only flow out from the tub's faucet-spout, not the shower-head. Then turn on the "hot" valve full-blast and wait till the faucet's chilly out-flow starts to turn warm before turning off the valve and moving the selector-knob over to "shower".
2. Step into the tub and properly close/arrange the curtain, then turn on the "hot" tap again and immediately hold your cupped hands up towards the shower-head so that its "initial" blast of water will hit your palms and spray sideways, rather than shockingly deluging your entire shivering "birthday suit" with the unheated "residual" water that's still inside the shower-head's feeder-pipe. Once the shower-head's spray warms, adjust the hot/cold valves for the desired water-temperature.