We could direct people to Wikipedia's list of cognitive biases (putting effort in to improving the articles as appropriate and getting a few people to add the articles to their Wikipedia watchlists). Improving Wikipedia articles has the positive externality of helping anyone who reads the article (of which the LW-curious will make up a relatively small fraction).

I think the ideal way to present rationality might be a diagnostic test that lets you know where your rationality weaknesses are and how to improve them, but I'm not sure if this is doable/practical.