Visual design is hugely important in the perceived quality of an app. It might even improve usability. Android is a great platform, but not all UI designers share this enthusiasm. Designing an app look and feel across different devices and screen sizes is a challenge. There is no set of resolutions to targets so you have to optimize graphics for different screen densities.
Optimize graphics for different screen densities. (Android Design)
High fidelity mock-ups are the best way to communicate visual design. Android Design Preview is a great tool that lets you mirror your desktop to your Android device. Really helpful – the Android Asset Studio library help in the design and development of Android application user interfaces.
