You're absolutely right. Keeping in mind what audience you're adressing is among the classical (and extremely useful) tips for improving one's writing.

To some extent what defines an "audience" is precisely what you can expect of them in terms of vocabulary, shared values, and so on. It seems difficult, then, to say how you might write specifically for "non-rationalists" - there is no such thing as a cohesive audience. But you could think about, say, what would work in writing about rationality for people who read CNN.com. (People who value being informed, might want to signal to others that they keep up with important world events, and so on.)

Less Wrong is a useful and informative blog, but, by and large, not if you aren't already a rationalist.

I don't think of myself primarily as a rationalist. I came here due to other interests; I like to learn about epistemology, ethics, AI, grand science-fiction themes like uploading and cryonics. OTOH I wouldn't be here if I wasn't interested in what a lot of rationalists are also interested in.