Since the longest possible exposure is the goal, a tripod is essential. This storm began at twilight, so I was constantly adjusting both time and aperture as we moved into night. By these exposures it was fully dark, and the exposure was ISO100, f/18 at 30 seconds with the 14-24mm lens at 14mm on a full frame sensor. (Nikon D700)
There is nothing more boring and meaningless than lightning bolts against a perfectly black sky, unless you have some kind of kinky fetish for squiggly lines. My goal is to achieve a believable shot of night in the foreground to put the lighting into context and give the viewer a sense of scale. I shoot on full manual, and make adjustments as the storm is moving in, then check the monitor frequently to fine-tune the balance between the normal environment and the lightning captured. I also shoot continuously and cull without mercy. I got dozens of shots with lighting in them tonight, but these were the only two I considered keepers.
I shoot 14-bit RAW in order to preserve the subtle gradients in the sky and foreground. I seek a white balance in processing that does not overpower the image with the ubiquitous toxic orange streetlights, but still maintains the look. Beyond f/11, there is a great deal of diffraction, softening the image and making it look like there is a star-filter mounted. Everything in photography is a trade-off, so I choose a long exposure and accept the diffraction. Again as a trade-off, I set a brief delay when I trip the shutter. It may miss the shot of the night, but what remains is tack sharp. The slight delay means that the tripod has become totally still, and the mirror is up and causing no vibration. These could be printed at enormous sizes.
Other than white balance, not much was done in processing. A touch of sharpening and a bit of perspective correction. HDR would be lovely, but that is not something that lightning grants one. Shadows are blocked and highlights are blown out, though I could have used the fill and recovery sliders to preserve a bit more. I tried, and it weakened the images.
By the way, fireworks and lightning share the same technique, with the only difference being that you can anticipate the fireworks, using a shorter exposure and a wider aperture so there is less diffraction.