Have you received a notification from Google via email or from within Webmaster Tools? Google is sending mass scale notifications warning sites that are not mobile-friendly that it will cause issues for them if they want to rank well for smartphone users.
This is a firm indicator that mobile-friendly factors will play a role in your websites performance in mobile search engine rankings. Already mobile users are able to distinguish a mobile-friendly website from search results…
Considering "Focus on the user and all else will follow" sits at the top of Google's core principles, website owners and businesses who are not enriching the viewing experience on their website for mobile users may eventually be penalized.
Is all about how a webpage is displayed on a mobile device, ensuring your website looks great on multiple devices.
Without special coding a standard web page will continue to render at a typical desktop screen width rather than scaling to fit the small screen size of a mobile or tablet.
A simple test you can perform from your desktop browser is to grab the side of the browser window and drag in so the width of the browser you are viewing becomes narrow. A mobile friendly or ‘responsive’ website will adapt to the changing browser width as pictured below…
Google has a new mobile friendly test tool that shows you what user experience (UX) features they are looking at around your site, it is likely these factors will be incorporated into Google’s algorithm updates if (or when) mobile friendly becomes a search engine ranking factor.
Plugins can prevent content from being usable on many platforms.
Configuring the viewport
Specifying a viewport matching the device's size allows content to render properly on all devices.
Sizing content to viewport
Ensuring page content fits horizontally within the specified viewport size, so the user is not forced to pan horizontally to view site content
Sizing tap targets appropriately
This encompasses buttons, links and form fields, that when placed too close together or sized too small makes it difficult for a user to easily tap on a touchscreen
Using legible font sizes
Sizing the text on your page to ensure it is legible and easy to read