Individual approach. It helps that I'm gluten-intolerant with a diabetic family and they know that I've learned a lot about nutrition that way.
Point out to the cook how delectable French cooking is.
Point out to the diabetic how their blood sugar spikes after eating grains, and then have them read Bernstein's book, which is the most sensible and approachable paleo-friendly book for the uninitiated I've seen.
Point out to close family that you're gluten-intolerant and that means they probably are too. Tell others that at least 30% of people are gluten-intolerant. Mention all the ways your health has improved.
If someone complains of a random gluten side-effect, jump on it! "I used to have the worst seasonal allergies in the world too, and dontchaknow they totally disappeared when I went GF! Weirdest thing. Apparently it's quite common, though. Because wheat is a grass, you know. And if you're allergic to grass, you shouldn't be eating it! Somehow "eating grass" aka wheat makes your immune system susceptible during allergy season."
If you know a paleo answer to their medical problem (obviously not while they're in a hospital bed recovering from a major scare), gently point it out. No preaching. "Dad, I just read an article about how gout is caused by fructose. Yeah, the fruit sugar. Yeah, I know they say it's the purines it meat, but apparently it's the way your liver processes sugar, makes crystals in your joints or something, and remember how well Atkins and South Beach worked for you? You never had gout then... I dunno, worth trying, isn't it?"
Finally, always stress how normal your diet is. I know some paleos like to eat a stick of butter in one sitting, but that's no way introduce the lifestyle to newbies! I eat hunks of meat, potatoes, veggies, generous helpings of cream and butter, and very modest amounts of sugar. Just no flour products, and most people are somewhat intolerant to them anyways, right? That's not so different from the mid-century American diet, is it? Or the European diet, and look how much healthier and blah blah blah.