Evidently, someone is passing around the idea that it is a good idea to start off the game by boxing off the four corners. That is, two lines in each corner, separating one square from the rest of the board. I've seen several people do this, without regard to who went first. And I find it frankly bizarre: how could it possibly be the case that boxing off the corners is always advantageous to you, and bad for me?
There is strategy to this game, but there is no universal strategy that works regardless of the circumstances, just because you're the one who is employing it. The strategy has to depend on whether you went first or second.
And on the board dimensions, of course!