If you're ever outside and see a thunderstorm coming, seek shelter immediately, either in a building or a hard-topped vehicle. These are designed to handle lightning strikes without harming the occupants.
Avoid taking shelter under trees; if a tree is struck by lightning, it will break and fall onto anyone below.
If you're in open water and see a thunderstorm coming, get to the land immediately. Being on the open water greatly increases your risk of being struck by lightning!