Smashing Magazine identifies six areas to consider for a great app.
1) The Idea. Find a vaccuum or empty niche for your app.
2) Money. Plan the business model for your app.
3) Define. Write down what your app will do in one sentence and stick to it.
4) Design. If the user has to think how to use the app, you’ve failed.
5) Coding. Native, high-quality, robust code is essential.
6) Marketing. Make friends, build buzz, launch big, love your fans.
But don’t simply read the above and move on. Check out the original article by Jeremy Olson at Smashing Magazine as it has plenty of further information for would-be app coders.