If you haven't read The Lean Startup, do so now. Treat your ideas for your mobile app as a hypothesis and try to validate it as quickly as possible. To summarize, use a Build->Measure->Learn development cycle. We always think we know what our customers want. But after investments of time and money, we find out that we were wrong. Make smaller bets!
One way to expedite this cycle is to use prototyping. Our designers and product managers really love Invision. You can quickly build prototypes, download them to a phone and do some quick user testing to get feedback.