To block my opponent's potential line of 4 pieces and set up future winning opportunities, I need to consider the columns where my opponent has already placed their pieces. Since my opponent has two X's in columns 1 and 2, I should place my O in one of the adjacent columns to potentially block their line and create a chance for myself to win. Column 3 seems like the best option as it is close to the existing X's and gives me the opportunity to potentially create a line of 4 O's in the future.