Tony Payne says:
Here's the test: someone who has denied themselves, who has taken up their cross and who wants to serve the gospel of Jesus makes their decisions in this order:
1. What's the best gospel work for me to be involved in?
2. Where do I need to live in order to share in that ministry?
3. What sort of job do I need to fund living in that place in order to do that ministry?
Let me be provocative and say that if you're making your decisions in the reverse order (i.e. 1. Which job? 2. Which house? 3. Which ministry?), then you haven't grasped the radical nature of the normal Christian life.
Read the whole thing, and I found the discussions that followed quite helpful too.
(Updated: Reformatted Tony Payne's quote)