We probably don't need to tell you that there's no way to guarantee that your app is going to make you rich. What we can do, on the other hand, is help you get a start in creating mobile app design that has greater potential to really catch on. Here are a few things that a lot of the top mobile apps have in common.
It's hard not to go viral when virality is built right into your app. Most games have this, with the option to automatically post high scores to Facebook and Twitter. Some apps allow users to post their own opinions and reviews to their social media feeds, or they focus on interpersonal activity, being most useful for groups of friends.
People talk about monetizing apps in somewhat ridiculous ways. Many games are free to play but with paid downloadable content. Gamers hate this. Some apps put in artificial roadblocks that force people to pay a dollar when they're halfway through with what they're doing. These are carny tricks. They get users to associate your app with a negative experience. Just charge a dollar or five or ten up front and be done with it, or give away a totally free version with ads and a premium version without. There's nothing to be gained from a nickel and dime approach to monetization, just play it straight.
The majority of popular apps, even those intended for serious purposes such as remixing music and so on, are built with user friendliness in mind. Ideally, your user should be able to grasp the entirety of your app within a few minutes of booting it up. We should only have to rely on the instructions as a last resort. Try to focus on intuitive interface and you'll have more people willing to recommend your app to their friends.
Finally, just focus on providing something that people will actually want. It's getting harder than ever these days to sell a bad product with creative marketing alone, so start with a great product and the marketing part will be relatively easy.