Draw the curtains so the dog can't see the flashes. If appropriate (not during an electrical storm) put the tv on with the volume low, to act as a distraction.
[header] How to help a dog overcome a fear of fireworks or thunder [title] Minimize the stimulation. [step] Insulate your dog from the bright lights and loud noises of storms and fireworks. Bring the dog indoors, and close all windows and doors.