I really rather like this article, although it is full of hidden assumptions, MovingTheGoalposts™, and irrelevant advice.
The number one Good Thing it points out is “Don’t Be Dumb.” This is not, strictly, functional advice to a Ubuntu user (who, let’s face it, has by definition installed Ubuntu), but it’s better than nothing … nothing being the default security setting for Ubuntu.
The number two Good Thing it points out (which is tangential to security, but excellent in other ways) is:
Back up regularly.
The great thing about Linux is that the Naughty Brigade can only trash your ...