Prove that it'll make money:

1. Call real people that would pay for it and talk to them about their needs. Do they describe what you're planning to do?

2. Build a simple email capture page (use something like LeadPages or OptimizePress to keep it cheap/easy) and write marketing copy to capture interest. Collect emails to see how interested your market is in the product.

3. Test. Tweak your copy based on feedback and repeat steps 1 & 2.

4. Once you have a legitimate amount of interest, you can either A) seek out a technical co-founder to build the app; B) write a business plan and pitch to potential investors; or C) bootstrap the business by hiring people out of pocket to build it for you.

5. Keep repeating steps 1–3 regularly to ensure you're still creating something people will actually use.

6. Release it with the minimum amount of features required to make it useful, then invite beta users to see how they use the app. Are they doing what you expected? Are they getting stuck anywhere? Do they need a feature you haven't considered yet?

7. Iterate.

Building an app is one of those simple-not-easy processes. A great app with no audience won't get far. A bad app with a huge audience won't last long.

If you'd like some help with creating a strategy, I'd be happy to share my prior experiences with bootstrapping companies and laying out business development plans.

Good luck!