UPDATE: We've published new guidelines for App Widgets for Android 4.0:
These include a PSD template package.
Although this isn't comprehensive, I have some PSD and PNG templates that may help with the visual design of app widgets:
Also, most design guidelines remain true for app widgets. I've put together some slides on design tips that can help.
Some more widget-related tips:
- Make sure the widget layout is accessible via directional (D-pad, trackball) navigation. There are still a lot of Android devices with directional navigation hardware.
- Make the widget deep links into your app when possible, for whatever content it is showing. If deep links don't make sense, the widget should at least jump into your app's home screen.
- Do not occupy an exorbitant amount of space—user's home screens are sacred, and you must respect them. A 4x4 or 3x3 app widget is rarely necessary.
- Offer a customization step during the widget-adding process if you have a lot of content.
- Don't refresh too often; be conscious of battery implications. If allowing users to customize the widget refresh interval, expose this setting in the app's settings, and not during the widget customization step.
- Be unique and be true to your brand, but adhere to system widget design themes and behavior. For example, customize the background color and show your logo, but use proper dimensions, shadows, and interactivity behaviors.