To string Christmas tree lights, first make sure the lights are all untangled and the ends are facing the same direction. Then, start from the top of the tree and work your way down, wrapping the lights around each branch and making sure to secure them with wire or clips. Try to distribute the lights evenly, and make sure not to overload any one branch with too many lights. Make sure to plug in the lights to check for any burnt-out bulbs or loose connections. Finally, add any other decorations like ornaments or tinsel.