This is my take on how to shoot lightning. You can find lots of information on the web about cameras and settings but these are the ones that work for me. You will need to test this information for yourself as each camera/film/lens combination is slightly different. Also remember to keep safe, we've all heard the stories of golfers who have been hit by lightning while playing the game. Consider a golf club as being the same as a camera/tripod.
1. If you can, visit the location during the day. It's much easier to frame your images when there is daylight.
2. Where to Focus ~ Focusing is going to be difficult at night if you don't have distance markers on your lens barrel. The best way to ensure sharp images of lightning is to focus at infinity, which is usually more than 30 metres from the end of your lens. Now if you don't have distance markers on the lens, simply set your camera on a tripod during the day and focus on an object 30 - 40 metres away. Then using a soft lead pencil, place a mark on the lens barrel and focus ring. Now when you align this mark you'll be focusing at infinity and you won't need to look through the view finder. While you're out doing this exercise you will probably notice that once you have the lens focused at infinity, the focus ring can still rotate a little further past this point. The reason for this it typically infrared light photography and is why you shouldn't rely on simply turning the focus ring all the way out. Mark the lens barrel, it's the safest way.
3. What ISO to use ~ Use a low ISO setting on your digital camera or film. I like to stay with 100 ISO. Remember, just because it's dark doesn't mean you need a faster film. You're photographing bright light, so a slower film speed/ISO is fine.
4. Aperture ~ The one that works for me is f5.6. Remember, you're focusing at infinity so depth of field is not playing an important role. What is playing an important role is the light collecting ability of the lens. You could go wider than f5.6 but this will impact the amount of lightning you can collect before the bright flashes become over-exposed. Getting this right will take a little practice but f5.6 is a great place to start.
5. Shutter Speed ~ You'll need the longest shutter speed you can get. If your camera supports 'B' or Bulb then use this. The settings I've given so far will result in multiple strikes in the image. You should be able to get at least 4 very bright strikes before you need to advance the film. If you are after single strikes, then you will need to open up the Aperture and speed up the ISO to ensure you get sufficient exposure for a single strike.
6. Cable Release ~ You will need a cable release for your camera. The exposure times are around 2 to 3 minutes. If you think you can stand behind your camera with your finger on the shutter button for that amount of time, over and over again... well, my hat off to you.
7. Tripod ~ you will need the sturdiest tripod you can find. Then you'll need to weight it down with something. Remember, with storms there is usually wind and with the lengthy exposure time you want to limit the vibration of the camera/tripod setup. I remove the shoulder strap from the camera or wrap is securely around the tripod to stop it blowing around in the wind. I also lean heavily on the tripod to keep it very still. If you have a backpack, consider strapping this to the tripod if you don't feel like standing out in a lightning storm with a metal tripod. Trying to take photos of lightning from within your car is a waste of time, in my opinion. The wind that comes with the storm is going to rock your car around far more than the tripod set up outside, resulting in blurred images. Even you moving around in the car will cause it to rock.
8. Shoot in RAW ~ If using a digital camera that supports RAW mode, use it.
Other considerations:
Safety: Lightning kills. If you're out in the open with a camera and tripod, remember that lightning can strike up to 16 kilometres ahead of the cloud bank. Don't ever consider yourself safe if you're out in the open photographing lightning. Wear a hat. Consider retiring to your car while the camera is doing its thing.
Rain: Protect your camera with a plastic bag around the camera. If it's raining heavily consider packing up for the night. The best time for lightning shots is before the rain starts. You have essentially clear visibility up to that point.
Autofocus: Remember to turn this off.
Useful tools:
Coffee or hot chocolate
Torch
Book
Radio
Waterproof jacket
Spare CF card, roll of film, batteries
Camera manual
Have fun, and let me know if these tips have been useful to you or if you have others that I can add.