This might seem obvious and simple, but anyone planning to do any decent walking on Tenerife should make sure that toenails are cut before setting off.
Many walks in Tenerife involve quite steep ascents, which isn’t a problem for the nails. But what goes up must come down and negotiating Tenerife’s volcanic slopes can have the toes pressed up against your boots like a Victorian orphan’s face at a restaurant window. If toenails are too long, descents can not only be uncomfortable, but there’s the possibility of longer term damage to nails.
So always remember to clip & snip before every trip.