Mobile First

Mobile first can refer to both the design strategy as well as the implementation of a responsive website, and its pretty much what it sounds like: you begin with the mobile design, which will be the simplest, and build it up as you add breakpoints for tablets, laptops and larger displays.

This approach is often considered ideal because the mobile design will force you to prioritize the site's goals with the greatest clarity since the real estate on a mobile device is the most limited.