Lights are one of the most important elements of decorating an outdoor tree for Christmas. To put lights on an outdoor tree, you will need to follow a few simple steps. First, make sure you have enough lights for the size of your tree. Then, start at the top of the tree and work your way down. Use clips or ties to attach the lights to the branches, making sure to space them evenly so the tree looks balanced. If you want to add some extra flair, you can also add ornaments or other decorations to the tree as well.