Before turning the water in a tub which has both spigot and shower, check if the toggle for the shower is on or off. Might be a good idea to also make sure the shower isn’t aimed at you.
When there is no hot water on the second night it may be better to not first think of the Internet reports of hot water outages in budget Vietnam hotels, but think instead if that unlabeled switch by the door is related. Might save you mentioning the hot water problem to the front desk and them explaining the reason for that switch.
When traveling with a tiny compass and a smartphone on which one has installed a map and carrying a paper map it’s a good idea to check one of them before starting your first bike ride. Or look at the sun, seeing as it always rises in the East. Or maybe just ask the person renting the bikes which way to town. If all else fails, one could notice all the other tourists are riding away from town while one is riding toward town.
When returning towels to the maid you requested because there were none in the room, probably best to not mention one of the first things you did in the room was photograph the towel swans.