The best first thing to ask is who is their person (singular) who is your contact and how often you can meet (weekly is a minimum, at least twice a week would be better -- schedule about 2-3 hours minimum for ongoing weekly meetings, about 2 hours for biweekly, and that's for normal/routine ones -- "big" ones whenever anything important happens, e.g. around milestones or any spec change, run longer).
The point is to make it sound so obvious that you'll be in continuous contact with a single person, who's speaking for the client in a single voice, that the only thing left to decide are who should that person be, and the best times and means for the very frequent meetings (VC, skype, google chat, AIM -- whatever you both like best and can adapt to).
If you don't set this core expectation for the project going forward you'll be stuck with a very unpromising project flow -- not may be stuck, will be stuck. You'll get a load of specs at the start (never complete enough, and yet many of them "goldplating" that the client doesn't really need or particular desire) and be expected to guess at far too many crucial details which you discover only as your work proceeds -- just too hard to get in touch timely with somebody at the client's who's empowered and willing to decide about that myriad details.
And when you do hear from the client, unless there's a clear agreement from the start about regular, substantial meetings with the Goal Donor (AKA Gold Owner;-), you'll hear far too many conflicting, contrasting voices contradicting each other -- and how can you decide who's just trying to make noise vs who's actually the decision maker for your project?!
Oh, and when suddenly nobody cares about feature X, I bet you won't learn about that and will waste a month of blood, sweat and tears implementing it (and maybe later more to rip it out because it's unused and just bloats the deliverable). Maybe you won't even hear (timely) when a new must-have feature Y suddenly appears on the scene, or previously-specified feature Z mutates into substantially-different feature T -- again, more and more wasted work for you, and at the same time increasing likelihood of reduced or zeroed-out final satisfaction on the client's part.
Once the "regular contact" feature of your development process is firmly nailed down, many other aspects that should be clarified, while each important, are minor in comparison.