We must always remember that we as chrisitians are to help bring the unchurched into the family of beilievers. If that were not so, then a christians mission would be rather dull and boring. The question of what to say to a athiest would depend on the person. I know people that I could do certain things and other people I would have to try another way. When there is someone I want to reach out to, I first pray then look for the right time.
Timing means a lot in reaching out to the unchurched.
I don't tell about my testimony or anything else untill they ask me. By them asking that leaves room for you to say more then by you right away tell them about you and them feeling bombarded by your story. When I have been asked, I will always mention Dr. Schuller and the Hour of Power and how much I have been helped by them. Each person is different and telling them about Christ will be different from person to person.