Icon Design Guidelines. An icon is a graphic that takes up a small portion of screen real estate and provides a quick, intuitive representation of an action, a status, or an app. When you design icons for your app, it's important to keep in mind that your app may be installed on a variety of devices that offer a range of pixel densities, as mentioned in Devices and Displays. But you can make your icons look great on all devices by providing each icon in multiple sizes. When your app runs, Android checks the characteristics of the device screen and loads the appropriate density-specific assets for your app. Because you will deliver each icon in multiple sizes to support different densities, the design guidelines below refer to the icon dimensions in dp units, which are based on the pixel dimensions of a medium-density (MDPI) screen.
Google I/O 2010 - Android UI design patterns. Balsamiq. DroidDraw : Graphical User Interface Editor for Android Cell Phone Development and Programming.