Actually, you know what? Simple answer here, and not to belittle or minimize in any way the previous replies/responses, (oops! sorry, a little disclaimer and apology on my part if I have which was purely unintentional), which in fact led me to an additional aspect as well.
Just ask and start discussions with the submissive. In advance if at all possible, starting with those early, tense emails on a Saturday afternoon, right?
Well, ok, back to the subject at hand here. Start those discussions early. Begin the process of letting him/her open up to you, like that first person you met during 7th grade Psych 101 class. You remember the classroom, the one with a black and white sign in the back of the room stating: "You are not paranoid if you think they are out to get you!" Ha!
Anyway, with discussions begun, you begin the necessary dialogue, and more importantly, start to build trust. Communication, especially of the intimate variety, such as here, is facilitated on so many levels beyond the written word. And, sometimes people insist on talking to a person prior to meeting. I think this blows the necessary tension, and dissipates any sense of suspense/fear/and anxiety. Don't do it...
And finally, find out what the submissive likes, what he/she prefers, when, and who much. They'll tell you quite a bit. Obviously, the rest of how this comes together, is up to you.