Another example of information "everyone knows" (but really doesn't), from Sara:
Watching my husband dress my daughter, I realized that my "standard" way of putting on tights, learned from my mother, might be obvious to me but not to everyone else. The basic trick to putting on tights or pantyhose is hold them at the top of one leg and sort of "walk" down the leg with the thumb and pointer finger, scrunching more fabric into your hand with each "step", until you get to the foot. You end up with a bunch of gathered material that you can pull over the foot in a quick move, and then use your hands to pull them part of the way up. Repeat on the other foot.