You can specify a maximum of three actions, each consisting of an action icon and an action name. Adding actions to a simple base layout will make the notification expandable, even if the notification doesn't have an expanded layout. Since actions are only shown for expanded notifications and are otherwise hidden, you must make sure that any action a user can invoke from a notification is available from within the associated application as well.
Notifications on Android Wear
Additionally, notifications and their actions are bridged over to Wear devices by default. Developers have control to control which notifications from bridging from the phone to the watch and vice versa. And developers can control which actions bridge as well. If your app includes actions that can't be accomplished with a single tap, either hide these actions on your Wear notification or consider hooking them up to a Wear app to allow the user to finish the action on their watch.
Bridging notifications
Notifications that should be bridged
    New instant messages
Don't bridge
    If a podcasting app has new episodes available for download, keep this notification on the phone.
Bridging actions
Actions to bridge
    Single tap actions such as +1, Like, Heart
Actions not to bridge
    Actions that map to features that aren't possible on the watch
Unique actions to define for Wear
    Quick lists of canned responses such as "Be right back"
    Open on phone
    A "Comment" or "Reply" action that brings up the speech input screen
    Actions that can launch Wear-specific apps
Heads-up Notification
When notifications with priority set to High arrives, it is presented to users for a short period of time on the device with an expanded layout with its actions exposed.
After this period of time, it retreats back to the Notification shade. If a notification is flagged as High or Max or a full-screen takeover, it gets a HUN in L.
Good examples of Heads-up notifications
    Incoming phone call when using device
    Alarm when using device
    New SMS message
    Low battery
Guidelines
Make it personal
For notifications of items sent by another person (such as a message or status update), include that person's image using setLargeIcon. Also attach information about the person to the notification's metadata.
Your notification's main icon will still be shown, so the user can associate it with the icon visible in the status bar.
Navigate to the right place
When the user touches the body of a notification (outside of the action buttons), open your app to the place where the user can view and act upon the data referenced in the notification. In most cases this will be the detail view of a single data item such as a message, but it might also be a summary view if the notification is stacked and references multiple items. If in any of those cases the user is taken to a hierarchy level below your app's top-level, insert navigation into your app's back stack to allow them to navigate to your app's top level using the system back button.
Correctly set and manage notification priority
Starting with Jelly Bean, Android supported a priority flag for notifications. It allows you to
influence where your notification will appear in comparison to other notifications and help to make sure that users always see their most important notifications first. You can choose from the following priority levels when posting a notification:
Priority    Use
MAX    Use for critical and urgent notifications that alert the user to a condition that is time-critical or needs to be resolved before they can continue with a particular task. Android系统英文文献和中文翻译(2):http://www.751com.cn/fanyi/lunwen_28864.html