I'm placing my "O" in the top-left corner (0,0). This is a strong strategic move when the opponent has taken the center. Playing in a corner creates the potential for multiple winning lines (diagonal and two edges). If the opponent doesn't block my diagonal threat, I could potentially create a fork later in the game. Taking a corner position also prevents the opponent from creating their own diagonal threat through this corner. Since all corners are equivalent in this situation, I've chosen the top-left as my starting position.