To decorate a Christmas tree with lights, start by choosing a color scheme or theme for your tree. This could be a combination of different colored lights or a single color scheme. Then, plan where you want the lights to go on your tree. It's best to start at the top of the tree and work your way down, making sure to evenly distribute the lights around the tree. Once you have a plan, begin to wrap the lights around the tree, making sure to keep them tight and secure.