Engineering

A large scale application requires not only problem solving skill set but also engineering best practices. Writing reusable and maintainable code is the key for a large scale development. Feature driven development, defensive programming, battle tested Android design pattern or continuous integrations you name it.

Problem Solving

Key to solve a large problem is to break it to smaller pieces and solve each sub-problems separately. On Android platform, so many device and active OS version make this is further complicated. Big challenge for Android platform is not to find a solution, but to find a solution which will work on every or most devices and OS versions.

Responsiveness

User loves responsive UI. App should interact with user always, Number of background process should never ever effect its UI responsiveness.

Fragmentation

One of the big hurdle for an Android developer is its fragmentations. API levels, OS version, millions of hardware's. And, let's not forget support and design support library. Defensive programming is the best way to go when to handle situation like this.

Memory Management

Now a days, when most device comes with gigabytes of physical memory an Android app have to work with it few MBs heap memory. And, so every bytes count.

Backend

On a small device like your mobile phones where every bytes count a RESTful backend API can help a mobile app function well on high demand situation. It can send only the data clients need. Proper pagination can improve UI responsiveness and request wait time.