1. How is your app going to shortcut some pre-existing habit or work for an individual?You can't add more work to the day. People just wont do it, and it'll be a struggle all the way. The only way you get to add work to peoples day is via legislation, or some kind of rule that has enforcement. Otherwise, people are lax and will forget to do it, or simple choose not to. Make sure they want to do it. The only way you can make sure of that, is to make some existing work easier.
There are some applications that seem like they've gotten around this theory, particularly in the social sphere. Arguably, social application are shortcutting communication and socialization. You're "reaching" 10x the people in the same amount of time, though you're giving up the human touch to do it.
The other question is:
2. Where's the money?Money is how apps get built, and how they survive. It's impossible to keep an application running if money isn't flowing in. This could be from any number of sources. Ads, subscriptions, one time purchases (not a good idea!), partners, or even some corporate sponsor.
Without a clear idea of where the money to build and maintain your application is going to come from in the long term, it probably wont get off the ground. Further, if it seems like you have an answer to this question that involves some kind of connection to an industry, you need to follow that up with, "Who has the connections to make this happen?"
If you can't answer these two questions clearly, concisely, and deeply, your idea needs more fleshing out before you can move forward. Unless you want to constantly be funding the app with your own time and money.
Once you can get past these two questions, refer back to my previous blog post for ideas on how to more deeply flesh out your idea!