From Confident Christianity - Pre-Evangelism
Conversation can take place at different levels, for example:
To do this we need more than one topic of conversation. Jesus and Paul could lead a discussion on virtually any topic to 'deeper things'. So we need to have well thought-out opinions on politics, economics, relationships, green issues or whatever, from a biblical perspective. Then Jesus and his own teaching can be brought into the conversation naturally.
Non-Christian thinking about the world is at odds with reality. By probing questions, we can find 'the points of tension' between the unbeliever's view of the world, and the world as it really is.
Francis Schaeffer taught that when we find such points of tension, we should gently push the conversation towards the logical implications of the non-Christian assumption that has been made. As we do this, it will become increasingly obvious that the world is not actually like that. Most people have not thought deeply about their non-Christian beliefs and it may well surprise them to hear their own thoughts as we encourage them to think out loud.
For a serious thinker, this can be a painful and distressing experience as the implications of what he is saying are exposed. Schaeffer referred to this as 'Taking the Roof Off'. 
None of this requires any 'God-talk'. Hopefully, after the stronghold has been brought down, there may well be an opportunity to discuss a different view of the world, which actually does justice to the richness and complexity of the world we find ourselves in. But that is to move on into evangelism!