HT Games
Understanding Strategy
One of the most important elements of learning a strategy for a game is understanding how strategy itself works. In game theory, strategy is used to look at all possible scenarios that may arise given each option, and pick the option with the greatest chance of a favorable outcome. In this case, tic-tac-toe strategy is an excellent beginning point, because there are a small and limited number of situations that can arise after every move. However, there are few perfect strategies, and the most common will show you how to win or force a draw every time.
Rules
First, a grid of four lines is drawn making nine squares. The goal is to get three markers of your type in a row vertically, horizontally or diagonally. X always goes first, and alternates turns with O until somebody wins or all squares are full, causing a draw. Once a space is full, it cannot be used again until the next game. After each game, players alternate their markers.
Strategy as X
In normal tic-tac-toe, X places their marker first. If you are playing as X, choose any corner spot and place your marker there. The next move will depend on O's move. If O moves to a corner, put your piece in any other corner. If O blocks, X plays on the final open corner. When O blocks, X strikes three in a row. If O chooses an edge, X plays the center square. When O blocks, two scenarios open up. Either block O, if need be, or place an X on the corner NOT bordered by an O. Two possible wins open up, you take the one she doesn't block. If O plays to the center square, X plays the corner opposite his first. Again, two situations arise. If O plays a corner, select the remaining corner and win on the next move. If O plays an edge and threatens a win, block and play down a draw.
Strategy as O
Though X has a clear advantage, you still have the opportunity to force a draw, or even win if your opponent doesn't think well enough ahead. If X plays his first piece to anything BUT the center square, play O on the center. If X plays to an edge that doesn't threaten a win, play to the corner opposite his original X. Block and draw. If X plays his two Xs on edge squares bordered by the same corner, play that corner, X will have to block you. Draw. If X plays two edges not bordered by the same corner, play a corner. X blocks, then you block X on the corner but set yourself with a win. X blocks only one, you win. If X plays his first two on any two corner squares, O should pick an edge, X blocks. Block and draw. If X's first move is to center, play a corner. If X threatens a win, block and draw. If she does not, play another corner. X blocks you, draw.
Perfect Strategic Game
Using this strategy, let's see what happens if both players follow the strategy. X plays a corner, O plays the center. X plays the opposite corner, O plays an edge, X blocks O's win. The two players play to a draw. This example shows why this strategy works for both sides. If it were unbalanced, one side could use the opponent's move to their advantage. In this case, they cannot. A draw with this strategy means that your opponent also knows what he is doing.