Google will soon start looking at how websites are presented on mobile phones to judge the value of the information in it*. This means that companies with more user-friendly mobile sites are more likely to rank higher in search engine results than those without good mobile sites. So, what can you do?
First, make sure that you have a mobile-friendly website, preferably responsive. Responsive sites are meant to look good in most display sizes (phone, tablets, small laptops, big screens).
Second, if you already have a mobile site or a responsive site, make sure that it actually looks good on a phone. If you use a template website it's super easy to just assume that your site will look good on a phone without any efforts, but sometimes you may add things to the desktop design that will look funky on a phone screen. So... test, test, test from an actual phone.
Third, make mobile work for you. Make sure that your email, phone number, and address are formatted on your site so users can click on them and email, call, or open navigation right from the site. The easier you make it for them to get to you, the better!
*Source: https://webmasters.googleblog.com/2016/11/mobile-first-indexing.html