As far as the impact on the ambience of a room, lighting is right up there next to music. If you have a fireplace, then a roaring fire is a must. With the exception of the dining room chandelier, overhead lighting should stay off, or at least be dimmed.
To create a warm environment, your lighting scheme should include multiple sources. Table and floor lamps illuminate conversation areas, while candles provide mood lighting throughout. If you want to add a lighting effect, use uplighting to highlight your Christmas tree or mantel décor.