I would say the attached - and Lone Signal ( http://www.lonesignal.com/ ) is already attempting to do so.
Also, Sanjoy: Did you have to use such a stereotypical depiction of an alien?
I would tell them to go to 4chan and wish them fare well because they would never visit after seeing it.
very hard question--it is sometimes hard enough to speak with a second or third cousin who may live 6000 miles away ---
I guess it would take multiple ways of description--all by my example and hope to have some commonality of understanding.
Very hard w/o knowing where to start--about the only things which come to my mind is to build commonality of trust and friendship ---and hope the alien does not view me as prey or "it" to be preyed upon?
I wish I could give a better answer. . . . . ..
Is there a youtube video of that conversation? Would be great to see!