leave the technobabble at the door
I've personally been in the web game for nearly 15 years, and after all that time I'm admittedly still surprised how often new clients view their website projects with such trepidation ... or rather, that they dread the prospect of having to sit down and "talk web".
There's no real mystery to it, I suppose. We're generally an enthusiastic crowd when it comes to extolling the virtues of AJAX, usability, Flash, or whatever centers our passion for the industry. The thing is, I've never met more than a handful of clients that had the remotest interest in what 'CSS' stands for. They get that there's a lot to the web, and they get that we know a lot about our industry. A client wouldn't be talking to us if they didn't have at least a little faith in our abilities. Throwing around big terms in order to impress upon them our knowledge is more likely to impress upon them that we need to get outside more often.
The way I avoid this is by focusing on the tangible things I need to do for the project, the stuff that they'll be able to relate to. I want to be talking "okay, we've mainly got an elderly audience, so I'd suggest we avoid drop-downs and any small or fussy controls". This kind of dialogue is going to be far more constructive, and one everybody can participate in.
Still, when meeting with new clients I do specifically ask them to make a rude face if I ever start to get too technical or begin using acronyms ("going geek", as one faithful client puts it). It's always safer to play with a net, after all.