In the 10 years I've been doing it, taking someone to the range and letting them shoot an AR15 has been the most effective means of conversion I've seen. I try to plan it firsthand so they can see for themselves some common myths ("high powered", effectiveness of "spray fire", accuracy of the system, times on self-defense target compared to other firearms etc.)
Most people, even gun people, have a lot of ignorance about guns and fearing what we don't know is a usual response. Taking someone shooting does two important things:
1. It helps them become informed and banishes the ignorance/fear
2. It makes them aware of how bad news coverage on firearms is and gets them to start questioning some of the BS masquerading as journalism.