Just recently a very nice man died suddenly. One of his relatives asked "Did he believe in Christ?" the answer sadly was "I am not sure."
This in itself would be motivation enough to start up a conversation with some one you may have a similar question about? If you are so motivated and have introduced each other the next step is to listen to them. What are they passionate about? What do they value?
This is the part of witnessing we forget about, to listen and then listen some more. Too often we feel it is "telling them ". That is why everyone gets turned off. Witnessing has a lot to do with you genuinely loving them and listening to their story. You can tell God's story later.
Its time to "walk across the room" remember pray before you do it.