Conversion is the work of the God. Our job is to be faithful in pressing unbelievers to the logical conclusions of their worldview. We must learn to listen if we are to debate faithfully. Let them talk, they will dig their own hole and fall right into it if you give them enough time. We must answer a fool according to what his folly deserves not according to his folly. In other words, don't respond to them in the same way they respond to you. Press them with questions like:
1) How do you know that is true? 2) Why do you think that? 3) What is your standard or authority for that view? 4) How does that make a difference in you life?