To hang Christmas lights indoors, you'll need some basic supplies: a ladder, a drill or hammer, a measuring tape, and some Christmas lights. First, measure the height of the ceiling and the width of the room. Then, decide where you want to hang the lights. Drill or hammer nails into the wall at the desired height and spacing. Finally, use the measuring tape to ensure your lights are evenly spaced. Once you're done, plug in the lights and enjoy the festive atmosphere!