> Leave the page at its default font size and avoid using custom fonts, preferring to use vague selections like “sans-serif” and “monospace”.
Why? These are all easily customizable by the user.
> Try not to use a purely visual representation of information, such as an icon: these should always be paired with text.
There are plenty of near–universally recognizable icons. Do your OS's windows say "close" in the title bar, or do they simply have an X?
> Also avoid moving information around — animations and visually complex state transitions.
Animations can be overused, but they can also serve an important purpose: displaying the transition between states.
For example, when you scroll your mouse, does the window just snap to the next page? Or does it go bit by bit so you can see where the new information comes from, and where the old information goes? Which do you think is a better experience?