Ask HN: Our iPad game hit top 30 in free games, how do we keep the momentum?

We are two MIT students who just published our physics-based puzzle game "Marble Drop" (http://www.marbledropgame.com) for iOS and Android (originally created for MakeGamesWithUs` MIT iOS games competition). The game has been a huge success in its first week, and we are now pushing the top of the App Store rankings in all of the relevant categories. At this point, we really have no idea what we should be doing as we try to grow our user base. We have been doing obvious things like talking to press, updating content, etc, but I suspect that there are a number of key strategies that are missing from our plan.

Do any HNers have advice on how we should spend our time and resources as we grow Marble Drop? Thanks in advance!