Pope Benedict XVI's Encyclical God is Love is a good start, it offers the once guiding principle that Christianity is an Encounter with a Person, Jesus Christ.
Being Christian is not the result of an ethical choice or a lofty idea, but the encounter with an event, a person, which gives life a new horizon and a decisive direction
The Gospels are the best way to get to know about Jesus and the shortest Gospel, Mark is the best one. A priest told a Cathechism class I taught that the thing that took him from business to the priesthood was reading Mark's Gospel on a trip one night, start-to-finish.
So it's gotta be a personal encounter and the Church helps. But the manual for conversion is the Bible and prayer (or spouses). That's one reason the Catholics don't go door to door proselytizing. The examples of authentically practiced Christianity should be enough for anyone to want to join up. Just shine, as the Newsboys' would say. Given the right circumstances, we'd be canonizing St. Mahatma Gandhi who said:
I like your Christ; I do not like your Christians. Your Christians are so unlike your Christ.
Which is the ultimate cop-out. If a person can't find enough good examples, there's always the Lives of the Saints, which is like, the best Christmas present for athiests.