tic tac toe - What is the optimal first move in tic-tac-toe?

I have been told that it is possible to guarantee no worse than a tie in normal 3x3 tic-tac-toe, but that the first move is very important. What is that important first move?

Answer

Tic-tac-toe has been solved. The optimal first move is to go in the corner.

As always, there is a relevant xkcd.