To decorate a Christmas tree with ribbon, start by choosing a color scheme. Then, cut the ribbon into different lengths to suit your tree size. You can also use different patterns or textures for added interest. Once you have your ribbon ready, begin by draping it around the tree in an X pattern, then move up and down the tree in a wavy pattern, tying it off at the top. You can also use the ribbon to create bows or other decorative elements to add more personality to your tree.