Google is now taking into account whether or not a website design is mobile-friendly or responsive on mobile devices when indexing for it's search engine. Basically, this means that website designs that are mobile-friendly and responsive will be ranked much higher than those that are not.
This change went into effect on April 21st back in 2015. They confirmed this year that they will be doubling up on that change in May 2016. This means that you need to make sure your website tests mobile-friendly according to Google's Mobile Friendly Test.
Take the test now, click on the button below. Make sure that your website does not have errors and that all resources are available.