Tripod, slow shutter speed and actually not as much luck as you'd think you might need. Last year I was doing a gig in the Czech Republic, we'd had flights cancelled so it was a long day and didn't arrive at the hotel until around 3 in the morning. A massive electrical storm hit just after we arrived and despite being very much not sober I couldn't resist trying to grab a shot from my hotelroom window. I just set it up to shoot 30 second exposures (as I didn't have a remote release to do any longer) and kept reeling off frames. With 30 seconds your chances of getting something in a fairly active storm are actually quite good!
This is what I ended up with, a fairly boring/generic composition but I was chuffed to get such a major bolt!
Lightning... by
Paul Nichols, on Flickr