Try searching for an app for either an Android or iOS device and you'll quickly find yourself wading through an absolute glut of apps. It's tough to stand out these days if you're app maker.

Some, of course, make their app free in hopes of gaining fast traction, but that move (obviously) tends to put a damper on ever making any real money.

To find out what works, I talked to Karim Morsy, the CEO of Algoriddim. His company makes an amazing app called Djay 2 that allows the user to create mixes of songs loaded on their iPad and then scratch using virtual turntables. The original version had a unique feature that took existing songs and created an "automix" of different songs.

For the Djay 2 release, the company redesigned the user interface, added a unique mode where you rotate the iPad to see only one turntable, included a brand new drum machine mode, and many other new features. Morsy says the best apps always have incredibly robust features--they show a finer attention to detail.

"Customers don't need another half baked to-do app or fart app," he says. "Your app needs to provide a unique, meaningful value to the customers. And you should never be discouraged if your idea is already implemented in an app."

Promoting the App

Once you've built a great app with robust features, it's time to start thinking about promotion. Morsy says it's too easy to rely on the Apple and Android "featured app" system, where your app gets highlighted for a few days. This can create high visibility for a while, but eventually your app won't be featured anymore.

"To achieve long-term success, you have to constantly improve the app, make it evolve with newer devices and technologies that become available, and continuously find new ways to get visibility," he says.

Algoriddim has quite an interesting plan for promoting its app. First, they partnered with high-profile hardware companies like Pioneer, Philips, Numark, and Vestax to create custom accessories for Djay 2. This promotes the app with each of those companies.

Second, they work with high-profile artists like David Guetta, Snoop Dogg, and Far East Movement. Each artist has promoted the app through their own social networks. Morsy says that has helped Algoriddim reach tens of millions of new customers. The artist connections are not just advertisements. There are "artist packs" available that add unique vocal and audio samples that are specific to the Djay 2 app.

Free or Not Free?

Many startups offer a free app initially, hoping to build up a customer base and then offer premium features once people are hooked. Morsy warns against trying to convert free customers over to paying customers. Algoriddim took the opposite approach. Originally, the Djay app sold for $49.99; the new app costs just $9.99. It's now one of the best-selling apps on the Apple store and has a 4.5 rating with customers.

Morsy says too many startups just make an app and then release it in hopes that customers will find it eventually. Good luck with that. He says every app at least needs a YouTube trailer video that explains how it works, a press release, and frequent social networking plugs. At the same time, for a paid app, you must continually keep improving it or you might see initial sales peter out and no long-term revenue.

"The mobile space and technology evolve very quickly, he says. "You have to constantly adapt to changing trends and leverage the latest technologies."