Google is changing how it’s ranking the websites again. Not only you need to create new content but has to be mobile friendly… more information from Practical Ecommerce website.
For WordPress Developers, this is not a big deal, because if you install Jetpack you already have a mobile option for your web, you only have to enable it. If you don’t have Jetpack installed, just click in Plugins->Add New and search Jetpack or click here to download it.
Click on the Mobile Theme Add On link, then configure your preferred options.
As a token of gratitude, if you can, enable the Mobile App Promos and Save Configuration.
But if you like to designs things by your own, then you need to make your site responsive. I have a very basic tutorial on this, hope this help.