One of the most profound spectacles in nature, an arc of lightning can appear to be the finger of God reaching down to earth. Capturing the image of this scientific phenomena can provide photographers with a frustrating set of challenges, though through careful preparation and a little trial and error, even the amateur photographer can produce high-quality images.
It should be noted that this type of photography is not for the beginner. The amateur, perhaps, but those just becoming familiar with apertures and shutter speeds will find that lightning photography requires a fairly intricate knowledge of camera mechanics. That paired with the numerous environmental considerations involved in this type of photography will probably be beyond the experience of those just starting out.
It's important to consider that the conditions for photographing lightning present challenges to any skilled photographer. Storms offer a degree of danger when considering lightning photography and the size, distance, angle, and brightness of the lightning stroke vary with each occurrence. Thus, in addition to practical knowledge, the art takes a bit of practice and learned skill.
To properly photograph lightning, you'll need: a sturdy SLR with a B setting; some digital cameras can accomplish this, but it's likely that you'll need a digital SLR rather than any of the fixed lens digitals; a lens capability up to 135mm; a cable release and tripod. Lenses should be f2.8 or larger, up to f22. If you are using a film SLR, you'll want ISO 100 or 200 depending on your distance from the anticipated stroke.
The purpose of using the B shutter is that it allows the camera to keep the lens open as long as you want, allowing the camera to have the stroke of lightning in focus and for exposure at the time you push the cable release for the shutter.
Considerations apply to conditions and to equipment. For lenses, it's important to understand your optics to the point of knowing whether or not you have coma possibility with a particular lens. Most of the upper end lenses don't have this issue, but a lot of Sigma and similar lenses will allow the lightning to blur and you'll never find a sharp picture. Further, low-hanging clouds and haze may mess with the lighting, so you'll need to factor these shots in and hope for a number of opportunities to adjust.
Finally, there are a number of advocates of daytime lightning photography, but I find that twilight seems to have the best conditions. The setting of lightning against the rosy hues of early morning or purple hues of sunset really make for an interesting exposures. In addition, the slightly darker setting allows for more contrast with the light and a better chance at sharp, clear lightning.