An excellent statement of intent from Mark. You can either read this now and start creating websites the right way, or you can scrabble to catch up further down the line; I recommend reading this now.
Embrace the fluidity of the web. Design layouts and systems that can cope to whatever environment they may find themselves in. But the only way we can do any of this is to shed ways of thinking that have been shackles around our necks. They’re holding us back.
Start designing from the content out, rather than the canvas in.
A website is not a magazine, though it might have magazine-like articles. A website is not an application, although you might use it to purchase products or interact with other people. A website is not a database, although it might be driven by one.
A nice round-up of responsible responsive web design techniques, ‘though I would go a bit further and suggest that the rallying cry is not so much about Mobile First but Content First.