QUOTE: “Well, I think you need to look at the pages in an overall way, you should look at the pages and say, actually we see this a lot in the forums for example, people will say “my text is unique, you can copy and paste it and it’s unique to my website.” But that doesn’t make this website page a high quality page. So things like the overall design, how it comes across, how it looks like an authority, this information that is in general to webpage, to website, that’s things that all come together. But also things like comments where webmasters might say “this is user generated content, I’m not responsible for what people are posting on my website,” John Mueller, Google 2016
If you are using Responsive Web Design, use meta name="viewport" tag to tell the browser how to adjust the content. If you use Dynamic Serving, use the Vary HTTP header to signal your changes depending on the user-agent. If you are using separate URLs, signal the relationship between two URLs by tag with rel="canonical" and rel="alternate" elements.