Be really rich, or rope in someone who is
Since you’ll have to hire designers and developers just to see the earliest version of your mobile baby, you'll need some seed money. Some experts advise starting out with at least $10,000. But odds are you'll need a whole lot more, thanks to a fairly lopsided supply/demand scenario that allows developers to essentially name their own price these days. If you want a more precise number, this site will give you a rough estimate of what you'll need to pony up.
Sketch it out, literally
No matter how clueless you are when it comes to design, you should patch together a rough idea of how you want the user interface to look. Seriously, just take some pen to paper and storyboard out how you see it functioning -- a designer can hammer out the details to make sure things flow in a logical and sophisticated way, but you should be able to bring a cohesive vision to the table.