Amusingly, John Wiseman's classic SAS survival handbook has advice for this situation.

  > You can sometimes sense that a lightning strike is imminent by a
  > tingling in the skin and the sensation of the hair standing on end. If
  > you are standing up, drop to the ground AT ONCE, going first to the
  > knees with the hands touching the ground. If you should be struck,
  > the charge may take the easiest route to the earth through your
  > arms - missing the torso and possibly saving you from heart failure
  > or asphixiation. QUICKLY LIE FLAT.