Google prepared a document with common mistakes while webmaster makes their websites mobile friendly.
- Unpayable Content
Few types of content or videos are not payable on mobile devices like a media that requires flash or other players which are not supported on mobile devices. When a user visits a page with unsupported content on a mobile device, they will see an error message. For animated content rendered using Flash or other multimedia players, consider using HTML5 animations that work across all web browsers. Google Web Designer makes it easy to create these animations in HTML5.
- Faulty redirects
If there are separate mobile urls, that must redirect mobile users on the desktop URL to appropriate mobile URL. There is also an option to find faulty redirects detect in the smartphone. Try using responsive web design, which serves the same content for desktop and smartphone users.
- Mobile-Only 404s
Some sites serve content to desktop users accessing a URL but show an error page to mobile users. Check the Crawl Errors report in Webmaster Tools; the Smartphone tab will show a list of detected URLs that return smartphone-only 404 errors.
- Cross Links
A common error is to have links pointing to an irrelevant page such as having the mobile pages link to the desktop site’s home page. Check your links to make sure that they point to the correct equivalent page.
- Slow Mobile Pages
Quick site load is a very important for mobile users. Users will be frustrated when site content is loading for a long time. Discover the page issues which make the page slow down using Google Page Speed Insights.