Before we start label the board in your head. Across the top is A through J, and down is 1 through 10.
Your first move is to put your piece at 4D, which should be diagonal to the top left of the top piece you start off with.
Next, put one directly to the right of that one, at 5D.
Now, block the computers diagonal at the bottom, most likely at 4G.
Then block the diagonal at the top. Which will either be 8C or 9B
Now put one in 6D, so that you have three in a horizontal row, after that put one in 4F to make a diagonal line of three.