1) Luck. Be at the right place at the right time. I was on a rooftop terrace looking west as a storm rolled in. And also, press the shutter at just the right time.
2) A camera. I almost always have a camera with me, even if it's a pocket point-and-shoot. Moments like this can arise unexpectedly, and I want to be ready to capture it.
3) Knowing the camera backwards and forwards. During fast-changing situations like this, you can't be fumbling around with the camera trying to figure out how to change the shutter speed or turn the flash off. Before you know it, the moment is gone. -Cort
Next Week's Theme: Independence