In reply to The Lemming:
As others have said; 30-second exposure, then just keep clicking until you get lucky.
As well as the lightning, try and make sure it's still a nice shot; try and get some interest in the foreground, hyperfocal distance to get as much in focus as possible and such-like.
The time of day and available light will obviously make a difference to what the final shot looks like - lightning at night doesn't tend to light much up other than clouds (unless it's particularly close).
My effort from Sardinia last year:
https://www.flickr.com/gp/durbs/o03BTw