Google has confirmed mobile friendly sites are search engine ranking factor. It will be work from April 21st 2015.
Primarily you can analyze your website in Google official mobile test tool. The following mobile tool provides status of your website and also provides mobile friendly suggestions to get better visibility in all mobile devices.
If your website is not mobile friendly you can update your website with responsive design and get full length mobile friendly guide here.
- Do not disallow images, CSS and java script in robots.txt.
- Font size should be readable without zooming in mobile devices.
- Make all pages mobile friendly.
- Get more suggestions in Google webmaster tools Search Traffic under Mobile usability option.