In this video Russ Weakley shows how to construct Media Queries using the Mobile First directive (i.e., coding from the smallest device width to the largest). Because Weakley advocates targeting content before targeting media, you may take exception to the following advice from the video narrative:

“Now for writing media Queries using the Mobile First strategy, small screen devices need to be served all the CSS without any Media Queries at all. The main reason for that is many mobile devices don’t support Media Queries. So what we need do is deliver our base CSS to all devices regardless of how sophisticate they are.”

You must decide what works for you. In the Responsive Web Design world, unfortunately, that are not yet many standards, so you have to make your own rules.