I've been meaning to try this for the holiday season. Maybe this year I'll do it. It looks really easy and really pretty. It's a surprising way to bring a glow to the fireplace and especially striking against a shiny floor. From an old craft magazine.
Wrap the first strand of lights around the ball as if you're winding yarn, rotating as you go. Connect the plug of the first string to the second strand of lights and keep winding. As you wrap the rest of the lights, use the same method, doubling back when you near the end of a strand so that all the cord connections are close together and easy to hide. You can use twist ties to help hold the strands in place. This is a casual, playful display, so go ahead and snake the cord out of the fireplace to plug it in.