Status indicators should use a style that is consistent with the text and menus present on the top panel. In general, these indicators should use colors in a considered and measured way. Icons and indicators must not change rapidly or abruptly (not more than once a second). Icon changes should transition smoothly.
Status Indicators should not be considered primary interaction points. Any action that is available through a status icon should also be accessible from elsewhere in the design. For example, network access must also be able to be configured through the system preferences / control-center. So, status indicators must not assume that the user can interact with them. They should only expect that they will be used to indicate status. There are a few reasons for this:
* On smaller form factor devices it may be difficult to interact with small icons
* When a high resolution pointer is not available it may be difficult to interact with small icons
* When the user has a disability the icons may be unusable for interaction
* Functionality must be able to be found by and be accessible to someone using desktop or control center search tools
Like all Top Menubar items, the icons should behave as if they are part of a menu-bar. The icons can be clicked with any mouse button but should always perform the same action no matter what button is used.
The order of system status indicators should be (from left to right):
Battery and power
In general, if you are not one of these you should probably not be using the System Status Area. Often the Message Tray is a better fit.
Specifically, things that should not be in the system status area:
* Chat or communication clients
* Software update notifications and reminders
* Music players
* New mail notifications
* CD/DVD burning progress
* Bug reporting system notifications
* Should offer limited, and common functionality
* Each should map to a tool in the System Settings
* Each should offer somewhat menu-like functionality on (left, right, middle, ...) click.
* The dropdown should animate from one to the next
Source from here