We are at a pivotal point in time in which traffic from many sites is primarily coming from mobile devices such as phones and tablets. Other devices to consider are smart watches, glasses, and televisions. For this reason, it is time to consider working with a mobile mindset when planning your responsive design. Develop your prioritized content, mockups, prototypes, and code for mobile devices first. Then work larger from there.
Embracing Mobile First Design by Garrett Heath