That's a great question! One of my favorite ways to outline windows with Christmas lights is to start by deciding what kind of look you want to create. Are you looking for a simple, classic look or something more elaborate and festive? You can use different colors and styles of lights to create a variety of looks.
Once you've decided on the look you want, the next step is to measure the windows and plan out the placement of the lights. You'll want to make sure the lights are spaced evenly and that there's enough of them to create the desired effect.