Many apps exists to enforce good UI design in Android Apps, some embedded in the developper settings screen. This app is a small simple app that you can add to your toolbox.
As you can see on the screenshot above, the app draws a grid above your Android UI, to let you see if your views are aligned following the design guidelines.
The project is Open Sourced on Github and can be downloaded on the Google Play Store
A couple of months ago, I stumbled upon pdf with an outline of Android phone / tablet (and other fruity devices too) used to design apps on paper before writing a line of code. For the curious, those files are still available online.
Today I found the ultimate tool for a designer : the Android Stencil Kit (and yes, they also have other OS covered too).
So yeah, it's my birthday soon, so I guess I'll make myself a gift...
Source: Spawn Rider