some general advice to avoid hypothermia are to dress with lots of layers, stay dry, get out of the cold as soon as you start to shiver, and ensure that there is adequate heating especially for elderly
children are in more danger than adults because they have less muscle
covering your head is important and will warm up your core
Your body loses 2-3 litres of water each day through sweating and urination, more if you are hot, exerting a lot of energy, or are at high altitudes. This water must be replaced. Therefore, drink often.
To prevent this rest, keep cool, stay in the shade, and seek shelter.