Stuff you'll need:
several sheets of white craft foam, exacto knife, cutting mat, globe string lights, white spray paint (optional)
(Optional): I bought my lights just after Christmas (clearance, hayoo!) so the cord was dark green. I lightly sprayed the cord with white Krylon Plastic spray paint. Now, it was real cold out here in Michigan so I impatiently put like, one coat of paint on the lights. They're really just less green... ;) If you're painting your lights, remove the bulbs and place a small square of painters tape over each bulb opening.
Using your exacto knife, cut your craft foam into 4"x5" rectangles.
Freehand cut your rectangles into stars. The knife seemed to cut easiest from the middle out to the edges.
Cut a small notch out of the center of each star.
Push each bulb through the notch and screw it back into the cord. And voila!