Be pragmatic in your atheism advocacy. Lay out your arguments why supernatural thinking is bad, both from an epistemological and pragmatic sense, poke at contradictions of the other person's religion with reality, and warn about the dangers of organized religion specifically, just don't cross the line of actually engaging in nuclear warfare.
If they haven't been brainwashed enough, they'll bite, even if it takes them months. If they have been brainwashed enough but they have intellectual honesty and curiosity, they may begin a self-questioning process themselves that will eventually make them crash, and it will be painful, but once they get recovered they'll be grateful. If they don't have that intellectual honesty, you've at least planted the potential seeds for them to decide at some later point that superstition was indeed bullshit, which may or may not come into fruition in the future. If the person you're talking with is an intellectual donkey (in terms of unwillingness to reason), you have nothing to gain from that conversation.
When it comes to old religious people, though, I limit myself to relentlessly attacking the church. Due to their material conditions, they have the lowest chance to ever leaving their beliefs anyway, so my goal is just to make them wary of any dumbfuck hate preacher they may find.