To decorate a Christmas tree, start by placing the tree in a corner or in a spot where it will be the focal point of the room. Then, begin by adding lights. You can use a string of lights or small, decorative lights. Next, add ornaments. Choose a color scheme or theme for your tree and decorate it with ornaments that match. Then, add tinsel or garland for extra sparkle. Finally, finish off the tree with a star or angel at the top.