How do you approach the matter

I gave a fairly successful talk at the Center for Inquiry's Student Leadership Conference this last summer on Bayes' Theorem and cognitive biases that was really a trojan horse for introducing fellow young atheists to the idea of rationality as an actual area of study.

one-to-a-small-roomful, with the general public

There were about sixty student group leaders of college and highschool atheist organizations in attendance.

how far can you expect to get?

Quantifying "fairly successful", I was approached afterward by at least six people who were interested in discussing my presentation and learning more. At least four more told me that they appreciated my presentation later that day or weekend.