Have you ever convinced a religious person to become atheistic? How did you do this? How long did it take? Were the people in some sort of life crisis, or were they just living along?
This is probably a quite difficult task of persuasion. So stories how people were successful at it could be very interesting to improve ones' persuasion abilities.
Relatedly, it might be interesting to know what religious groups have gathered on techniques to convert people to their religion - are there some manuals/techniques floating around?
A number of commenters have referenced the idea of being a spectator instead of a target, and I think this is important. One-on-one debates often have a competitive aspect to them that can make people defensive (nobody wants to feel like they've "lost" the "argument").
And really, converting people on a case-by-case basis is probably one of the least efficient approaches to cultural change. My guess is that it's more important to create a healthy "atmosphere for conversion", and I think a big part of that is just being outspoken and unashamed about your atheism. The more people do that, the more it'll be normalized - exposure>persuasion. The arguments are all out there anyway. When someone is ready, they'll seek them out, whether that's talking to atheist friends, watching youtube videos, reading books, or whatever.
And for the record, my own transition occurred in my mid-twenties, somewhere between starting an introduction to philosophy book and finishing Michael Shermer's "Why People Believe Weird Things".