To decorate your mantelpiece for Christmas, you'll want to start by adding some festive greenery. Consider using a bough of holly or pine branches with red berries for a classic holiday look. Add a few Christmas ornaments and lights to complete the look. If you want to take it a step further, you can add some stockings or garlands to the mantel, along with some snowflake-shaped decorations. Lastly, don't forget to add some Christmas scents, like cinnamon or pine, for an extra festive touch.