Darryl Dash has posted an interview (second of two parts) with Tim Keller (HT: Steve McCoy) that is well worth reading. I thought Keller's answer to the question below was especially wise and helpful.
How do we change in order to contextualize without changing the gospel?
That is the practical question in ministry. If you under-contextualize your ministry and message, no one's life will be changed because they'll be too confused about what you are saying. But if you over-contextualize your ministry and your message, no one's life will be changed because you won't really be confronting them and calling them to make deep change.
If this scares you and you say, "Well then let's not even try it," then you have to remember something: to over-contextualize to a new generation means you can make an idol out of their culture, but to under-contextualize to a new generation means you can make an idol out of the culture you come from. So there's no avoiding it.
There's far more to say about this subject, but I'll just give you one bit of advice. The gospel is the key. If you don't have a deep grasp on the gospel of grace, you will either over-contextualize because you want so desperately to be liked and popular, or you will under-contextualize because you are self-righteous and proud and so sure you are right about everything. The gospel makes you humble enough to listen and adapt to non-believers, but confident and happy enough that you don't need their approval.