Google is looking for a “website that is well cared for and maintained” so you need to keep content management systems updated, check for broken image links and HTML links. If you create a frustrating user experience through sloppy website maintenance – expect that to be reflected in some way with a lower quality rating. Google Panda October 2014 went for e-commerce pages that were optimised ‘the old way’ and are now classed as ‘thin content’.
QUOTE: “Supplementary Content contributes to a good user experience on the page, but does not directly help the page achieve its purpose. SC is created by Webmasters and is an important part of the user experience. One common type of SC is navigation links which allow users to visit other parts of the website. Note that in some cases, content behind tabs may be considered part of the SC of the page.” Google Search Quality Evaluator Guidelines 2017

I think the anchor text links in internal navigation is still valuable – but keep it natural. Google needs links to find and help categorise your pages. Don’t underestimate the value of a clever internal link keyword-rich architecture and be sure to understand for instance how many words Google counts in a link, but don’t overdo it. Too many links on a page could be seen as a poor user experience. Avoid lots of hidden links in your template navigation.
QUOTE: “alt attribute should be used to describe the image. So if you have an image of a big blue pineapple chair you should use the alt tag that best describes it, which is alt=”big blue pineapple chair.” title attribute should be used when the image is a hyperlink to a specific page. The title attribute should contain information about what will happen when you click on the image. For example, if the image will get larger, it should read something like, title=”View a larger version of the big blue pineapple chair image.” John Mueller, Google
Search engine optimization (SEO) is often about making small modifications to parts of your website. When viewed individually, these changes might seem like incremental improvements, but when combined with other optimizations, they could have a noticeable impact on your site's user experience and performance in organic search results. You're likely already familiar with many of the topics in this guide, because they're essential ingredients for any web page, but you may not be making the most out of them.
QUOTE: “Sitemaps are an easy way for webmasters to inform search engines about pages on their sites that are available for crawling. In its simplest form, a Sitemap is an XML file that lists URLs for a site along with additional metadata about each URL (when it was last updated, how often it usually changes, and how important it is, relative to other URLs in the site) so that search engines can more intelligently crawl the site.”
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