PLEASE PIN!!
Here is one way to almost always win this game!
Step 1: Place O or X in any corner.
Step 2: make sure player 2 or 1 puts it in the middle, or the opposing corner or any box that is not going to be used.
Step 3: Put O or X on the right side or left side of the first one you placed.
Step 4: make sure they don't block you in any of the right or left side, even if it wasn't filled with anything of yours yet.
Step 5: Put O or X on the other spot and then, if they they try to stop you from the win, it's basically game over for them, place it and you win!
Enjoy!