Bet you never thought the iPhone would grow so alarmingly popular. But it has, and we cannot simply ignore it or the millions of applications that float in the Apple App Store.

From funny to unique, unique to unusual and bizarre, diverse kinds of applications rule the App Store. Hundreds of more such are launched everyday. With the App Store growing bigger and bigger everyday, the lifetime of an ordinary app denigrates to less than a week. Making a breakthrough iPhone app is indeed a challenge all iPhone application developers face.

To launch a top-selling iPhone app is no easy job and requires a lot of racking your brain. Though there is no exact science to build a killer iPhone app, you can launch a near-perfect top seller if you follow these 7 rules of the thumb:

1. Innovate: Try something novel. Does your iPhone app have the “wow” factor? Is it innovative, out of the ordinary? Is it the only one in its kind? If yes, your app will definitely get due recognition in the App Store.

2. Make it usable: Your apps can be extraordinarily creative and startlingly new. But users are going to keep it idle if it is not usable. Build an app which has utility value. Fancy apps are good, but they don’t get you anywhere. A usability specialist says that one should follow Apple’s sterling virtue of “intuitive and consistent usability” while building apps for the iPhone.

3. Keep it Simple: Keeping it simple is a golden rule in mobile application development. No one wants an app that confuses or complicates things for them. The more difficult you make your app for usage, the less recognition it is going to receive from users.

4. Pricing: Anything sells if given for free in the Internet world. This does not mean you need to give your killer app for free. You can price it anywhere between $0.99 to $20. But, act prudently. Your app will get more exposure when given for free than when launched with a price tag. Maybe you can try different strategies. You can give your beta version for free and put a price on newer versions.

5. Provide Support: Be responsive to how your app performs in the store. If users are having difficulty in handling some feature, try to change it or post guides on how to handle your app.

6. Upgrades: Anything left idle grows stale. Never leave your app in beta. Keep upgrading new features. Listen to your users and add as many new features as possible. People who failed notice your app during its launch may notice its upgraded version and start using it.

7. Marketing is must: Yes, without doubt, this is important in killer-app making. You cannot create a killer app if you fail to market it. The more your app is marketed, the more it gets noticed by users. Instead of aggressive marketing, engage in useful, result-oriented marketing. You’ll definitely hit the road to success.