My cameras have an intervalometer built into the menus. I set an interval between shutter trips, how many shots I want, then set a long-ish shutter speed, good aperture and ISO, and let it run on the tripod. My interval is 2 seconds longer than the shutter speed I use, so a series of 15 second exposures would be started 17 seconds apart. Going down to 16 seconds (1 second after the previous shutter-close) sometimes gets missed shutter openings and the shutter doesn't open until the next interval elapses,possibly missing a bolt.
I usually use ISO 400 and
f:4 or
f:5.6. The zoom setting I use depends on how widespread the lightning is around my spot. if it's all over the sky, I'll shoot zoomed fully back and crop the images if needed. If the lightning is all "right over there," I'll tighten up on that space for higher resolution in the final shots.
I posted my last set
here.
If you don't have an intervalometer, either built-in or add-on, you can use a remote trigger for your shutter and take the shots manually, hit it when you see the flash. If the lightning is worth shooting, it lasts longer than the instant of your reflexes, although an actual trigger device is still better. With the intervalometer, unless the storm is really busy electrically, you will get a LOT of dark frames, but in the digital age, who cares? If you're buying film, that's a different story!!