1) Building a relationship, even if it's a brief one (I spent less than 10 minutes doing that) before talking about god/religion is probably worth the while. I'm no fan of "seeker-sensitive" strategy of some churches, but on a personal level, as a general rule, I would try to have some casual chat before getting into the gospel.
2) If possible, lead him to talk about his opinion on god and start from asking his point of view and opinion on god, genuinely asking about his god. This is probably not a hard rule I'd follow all the time, but if he/she mentions god or religion before I do, and I hear him out for long enough, he will generally hear me out on the Christian God as well.
3) Avoid talking about "religion" if possible in order to focus on god, rather than the institutions and human failings in presenting god. So often the argument goes like "it is because of the church, I don't believe in God." Sometimes their accusation against the church is legitimate, sometimes they are misinformed and misguided. Rarely they would mention some good works churches do, like charity works. Church should strive for purity and charitable works so that it will not only stop hindering people from believing, but also to positively represent the gospel and the work of God as an effective witness. However, regardless, I think it is more urgent and effective to present the truth of the gospel than to defend the church and attack the other religions when talking to an unbeliever because talking about religion will often distract us from discussing god-matters to people-matters. To do that, I'd try to stay on the topic of god, ie. theology (of both Christian and pagan) until the presentation of gospel and God is done, rather than talk about what kind of practical differences there are, even if they are
4) Remember to listen carefully so you can "capture and frame" his/her argument (opinion about god) without becoming argumentative. By "capture" I mean that you should understand what his arguments are and what they mean in relation to god. By "frame" I mean that you should bring him to see that his own argument breaks down by another of his own understanding/arguments on the topic of god, ie. theology. This I believe is far better than trying to break his argument with MY arguments. When one sees there is inconsistency within his own understanding, he will have to reconsider and re-construct his own understanding in order to remove the inconsistency. This may lead to change of his worldview in a positive way, and lead him to investigate more and end up trusting in the Lord. However, I am aware that even if one sees an inconsistent element in his worldview, it may not lead him to re-construct his worldview when he is deceived by post-modernism. It's a rotten generation we are living in.
But then of course, above all, if God does not work, all our sweat and labour are in vain. Without Him, it's totally useless and you will never EVER see a lasting effect. So, pray.