This sounds like you think of them as mooks you want to show the light of enlightenment to. The sort of clever mathy people you want probably don't like to think of themselves as mooks who need to be shown the light of enlightenment. (This also might be sort of how I feel about the whole rationalism as a thing thing that's going on around here.)

That said, actually being awesome for your target audience's values of awesome is always a good idea to make them more receptive to looking into whatever you are doing. If you can use your rationalism powers to achieve stuff mathy university people appreciate, like top test scores or academic publications while you're still an undergraduate, your soapbox might be a lot bigger all of a sudden.

Then again, it might be that rationalism powers don't actually help enough in achieving this, and you'll just give yourself a mental breakdown while going for them. The math-inclined folk, who would like publication writing superpowers, probably also see this as the expected result, so why should they buy into rationality without some evidence that it seems to be making people win more?

Taboo "rationalist". That is, don't make it sound like this is a group or ideology anyone is joining (because, done right, it isn't.)

Discuss, as appropriate, cognitive biases and specific techniques. E.g. planning fallacy, "I notice I am confused", "what do you think you know and why do you think you know it?", confirmation bias, etc.

Tell friends about cool books you've read like HPMoR, Thinking Fast and Slow, Predictably Irrational, Getting Things Done, and so forth. If possible read these books in paper (not ebooks) where your friends can see what you're reading and ask you about them.

The problem with rationality is that unless you are at some level, you don't feel like you need to become more rational. And I think most people are not there, even the smart ones. Seems to me that smart people often realize they miss some specific knowledge, but they don't go meta and realize that they miss knowledge-gathering and -filtering skills. (And that's the smart people. The stupid ones only realize they miss money or food or something.) How do you sell something to a person who is not interested in buying?

Perhaps we could make a selection of LW articles that can be interesting even for people not interested in rationality. Less meta, less math. The ones that feel like "this website could help me make more money and become more popular". Then people become interested, and perhaps then they become interested more meta -- about a culture that creates this kind of articles.

(I guess that even for math-inclined people the less mathy articless would be better. Because they can find math in thousand different places; why should they care specifically about LW?)

As a first approximation: The Science of Winning at Life and Living Luminously.

How about bringing up specific bits of rationality when you talk with them? If they talk about plans, ask them how much they know about how long that sort of project is likely to take. If they seem to be floundering with keeping track of what they're thinking, encourage them to write the bits and pieces down.

If any of this sort of thing seems to register, start talking about biases and/or further sources of information.

This is a hypothetical procedure-- thanks for mentioning that The Simple Truth isn't working well as an introduction.