The best way to put Christmas lights on windows is to start by preparing the windows with a clean surface. Then, use a ladder or step stool to reach the top of the window and start from there. Make sure to secure the lights to the window frame or ledge using hooks or tape. Then, work your way down the window, ensuring the lights are evenly spaced out and straight. Make sure to test the lights to make sure they're working properly before turning them off. If you have any extra lights, you can also use them to decorate other areas of your home for the holidays!