Stay indoors as much as possible, especially the elderly and very young. 

Several layers of loose-fitting, lightweight clothing will do better at keeping you warm than just one, big jacket. Start with a long-sleeve undershirt or turtleneck, then throw on a sweater, followed by your outer coat that should also be water repellant. If it's extremely cold, don't forget the long underwear.

Make sure to wear a hat to cover your ears, gloves to keep you fingers warm, and fur-lined boots for your feet and toes. Your body prioritizes your inner-core, so your extremities will feel the cold first. Quite literally. 

Hypothermia can happen quickly. Look out for uncontrollable shivering, slurred speech, disorientation, and incoherence, among other signs. If your core body temperature drops below 95 degrees, seek immediate medical attention.

If you do need to be outside, look out for frostbite. If you notice a pale appearance or a loss of feeling in your extremities, seek medical attention immediately.