It's not easy staying warm... My climate doesn't get as cold as some places, but the cold is damp cold, which feels colder than a much colder dry cold.
Making matters worse, I live in a place that is poorly insulated, and has electric heat. So I keep the thermostat low when I'm up, and even lower when I'm in bed or leave on errands.
Like Lawrence above, I drink a lot of tea (and coffee), and tend to eat warm meals. I wear a warm sweatsuit when I'm staying in. A hot bath, even with a small quantity of water, helps to warm me up. I also keep a blanket in the living room to wrap up in.
When going out, it's easier...since most places I go to are heated better, and so all I need to worry about is the time I'm actually outside...