A Toolbar is useful for providing users with quick access to an app's most used features. Besides Buttons, a Toolbar is one of the most frequently used UI elements. It may seem like a simple container, but it is important to remain consistent in it's use and organization.

Ordering Toolbar Items

Toolbar items should be organized with the most significant objects on the left and the least significant on the right, with the AppMenu always on the far right of the Toolbar. If you have many toolbar items it may be appropriate to divide them into groups with space in between each group.

Allowing for Customization

Although it's not required, you may feel that your app should be flexible with its UI. In the case of a file browser or web browser, this means the ability to hide and show different panes as well as the ability to rearrange toolbar items. This kind of functionality should be provided by a context menu on the toolbar. The menu should first display UI elements that can be shown or hidden, then a separator, and finally the Customize... entry like so: