What to do first when boat runs aground?

Lighten ship; people need to get off so that you don't damage the hull further. What did you run aground on, rocks or sand and dirt? If rocks, check immediately for leaks; you don't want to get back out into deep water and THEN sink. If it's a small boat, do you have a diving mask? Can you check the outside of the bottom of the boat and see if there's any damage?

In any event, you probably want to get back to port or the dock and do more thorough inspections there.