To shoot lightning you either have to have a whole lot of it or extremely lucky. Last night we had a fair amount of lightning (no thunder) and I must have had luck on my side because I got a decent number of shots. I shot approximately 95 frames and got 16 good shots, while this isn't a great ratio for normal shots, for lightning it is pretty good.
I was shooting out my window with a Canon T4i with an 18 – 200mm lens mounted on a gorilla pod. The camera was set at an ISO 200 and I alternated between an aperture of f/9 and f/11 with a shutter speed between 5 – 15 seconds. It appeared that the sweet spot was f/9 at 6 seconds. However there was still a lot of luck involved capturing lightning bolts.