Look at the notification icons Android apps already provide and create notification icons for your app that are sufficiently distinct in appearance.
Use the proper notification icon style for small icons, and the Material Light action bar icon style for your action icons. Do not place any additional alpha (dimming or fading) into your small icons and action icons; they can have anti-aliased edges, but because L uses these icons as masks (that is, only the alpha channel is used), the image should generally be drawn at full opacity.
Keep your icons visually simple and avoid excessive detail that is hard to discern.
Use color to distinguish your app from others. Notification icons should only be a white-on-transparent background image.
Pulse the notification LED appropriately
Many Android devices contain a notification LED, which is used to keep the user informed about events while the screen is off. Notifications with a priority level of MAX, HIGH, or DEFAULT should cause the LED to glow, while those with lower priority (LOW and MIN) should not.
The user's control over notifications should extend to the LED. When you use DEFAULT_LIGHTS, the LED will glow with a white color. Your notifications shouldn't use a different color unless the user has explicitly customized it.
Building notifications that users care about
To create an app that users love, it is important to design your notifications carefully. Notifications embody your app's voice, and contribute to your app's personality. Unwanted or unimportant notifications can annoy the user or make them resent how much attention the app wants from them, so use notifications judiciously.
When to display a notification
To create an application that people enjoy using, it's important to recognize that the user's attention and focus is a resource that must be protected. While Android's notification system has been designed to minimize the impact of notifications on the user's attention, it is nonetheless still important to be aware of the fact that notifications are interrupting the user's task flow. As you plan your notifications, ask yourself if they are important enough to warrant an interruption. If you are unsure, allow the user to opt into a notification using your apps notification settings or adjust the notifications priority flag to LOW or MIN to avoid distracting the user while they are doing something else.
While well behaved apps generally only speak when spoken to, there are some limited cases where an app actually should interrupt the user with an unprompted notification.
Notifications should be used primarily for time sensitive events, and especially if these synchronous events involve other people. For instance, an incoming chat is a real time and synchronous form of communication: there is another user actively waiting on you to respond. Calendar events are another good example of when to use a notification and grab the user's attention, because the event is imminent, and calendar events often involve other people.
When not to display a notification
There are however many other cases where notifications should not be used:
Avoid notifying the user of information that is not directed specifically at them, or information that is not truly time sensitive. For instance the asynchronous and undirected updates flowing through a social network generally do not warrant a real time interruption. For the users that do care about them, allow them to opt-in.
Don't create a notification if the relevant new information is currently on screen. Instead, use the UI of the application itself to notify the user of new information directly in context. For instance, a chat application should not create system notifications while the user is actively chatting with another user.
Don't interrupt the user for low level technical operations, like saving or syncing information, or updating an application, if it is possible for the system to simply take care of itself without involving the user. Android系统英文文献和中文翻译(4):http://www.751com.cn/fanyi/lunwen_28864.html