Prefer concise and explicit messages.
Avoid using two lines of text for a message. Never show more than one fixed banner.
Always show at least a title or add secondary text or an icon to provide more details. You also add a call to action if the user can perform an action quickly.
Be careful with using too many floating banners at the same time, it increases the cognitive load for the user.
Always use a description and propose actions when there are several floating banners of the same type to keep the user informed.
Avoid technical and unexplicit messages for the user.
Float banners always overlay the content.