I ask if they're a trial. If yes, i then ask if they know about the trial account addon, if no, and they're interested, i either point them in the right direction to download it, or i'll walk them through how addons work. I hate trying ( and failing sometimes) to explain how addons work and how to install them, mostly because i don't remember where all the files are on older windows operating systems, and i know nothing at all about other operating systems. Typically, if they're interested, they are really grateful you even spoke to them, let alone helped them out.
Edit, Also, like Kincaide said, if you lead with "There is a whole community of trial accounts that chat, premade for BGs and run dungeons" they will be pretty interested. Most people don't like playing alone. You will run into fully geared twinks who know what they are doing, but still don't wish to join, which is -okay- too.