In 2007, Google announced a campaign against paid links that transfer PageRank.[30] On June 15, 2009, Google disclosed that they had taken measures to mitigate the effects of PageRank sculpting by use of the nofollow attribute on links. Matt Cutts, a well-known software engineer at Google, announced that Google Bot would no longer treat any nofollow links, in the same way, to prevent SEO service providers from using nofollow for PageRank sculpting.[31] As a result of this change the usage of nofollow led to evaporation of PageRank. In order to avoid the above, SEO engineers developed alternative techniques that replace nofollowed tags with obfuscated JavaScript and thus permit PageRank sculpting. Additionally several solutions have been suggested that include the usage of iframes, Flash and JavaScript.[32]
QUOTE: “The score is determined from quantities indicating user actions of seeking out and preferring particular sites and the resources found in particular sites. *****A site quality score for a particular site**** can be determined by computing a ratio of a numerator that represents user interest in the site as reflected in user queries directed to the site and a denominator that represents user interest in the resources found in the site as responses to queries of all kinds The site quality score for a site can be used as a signal to rank resources, or to rank search results that identify resources, that are found in one site relative to resources found in another site.” Navneet Panda, Google Patent

Google has a LONG list of technical requirements it advises you meet, on top of all the things it tells you NOT to do to optimise your website. Meeting Google’s technical guidelines is no magic bullet to success – but failing to meet them can impact your rankings in the long run – and the odd technical issue can actually severely impact your entire site if rolled out across multiple pages.
Think about how Google can algorithmically and manually determine the commercial intent of your website – think about the signals that differentiate a real small business website from a website created JUST to send visitors to another website with affiliate links, on every page, for instance; or adverts on your site, above the fold, etc, can be a clear indicator of a webmaster’s particular commercial intent – hence why Google has a Top Heavy Algorithm.

Keep resources crawlable. Blocking page resources can give Google an incomplete picture of your website. This often happens when your robots.txt file is blocking access to some or all of your page resources. If Googlebot doesn't have access to a page's resources, such as CSS, JavaScript, or images, we may not detect that it's built to display and work well on a mobile browser. In other words, we may not detect that the page is "mobile-friendly," and therefore not properly serve it to mobile searchers.
QUOTE:  Each piece of duplication in your on-page SEO strategy is ***at best*** wasted opportunity. Worse yet, if you are aggressive with aligning your on page heading, your page title, and your internal + external link anchor text the page becomes more likely to get filtered out of the search results (which is quite common in some aggressive spaces). Aaron Wall, 2009

QUOTE: “Shopping or financial transaction pages: webpages which allow users to make purchases, transfer money, pay bills, etc. online (such as online stores and online banking pages)…..We have very high Page Quality rating standards for YMYL pages because low-quality YMYL pages could potentially negatively impact users’ happiness, health, or wealth.“
QUOTE: “Cleaning up these kinds of link issue can take considerable time to be reflected by our algorithms (we don’t have a specific time in mind, but the mentioned 6-12 months is probably on the safe side). In general, you won’t see a jump up in rankings afterwards because our algorithms attempt to ignore the links already, but it makes it easier for us to trust the site later on.” John Mueller, Google, 2018
QUOTE: “Another problem we were having was an issue with quality and this was particularly bad (we think of it as around 2008 2009 to 2011) we were getting lots of complaints about low-quality content and they were right. We were seeing the same low-quality thing but our relevance metrics kept going up and that’s because the low-quality pages can be very relevant. This is basically the definition of a content farm in our in our vision of the world so we thought we were doing great our numbers were saying we were doing great and we were delivering a terrible user experience and turned out we weren’t measuring what we needed to so what we ended up doing was defining an explicit quality metric which got directly at the issue of quality it’s not the same as relevance …. and it enabled us to develop quality related signals separate from relevant signals and really improve them independently so when the metrics missed something what ranking engineers need to do is fix the rating guidelines… or develop new metrics.” SMX West 2016 – How Google Works: A Google Ranking Engineer’s Story (VIDEO)

While the title tag is effectively your search listing’s headline, the meta description (another meta HTML element that can be updated in your site’s code, but isn’t seen on your actual page) is effectively your site’s additional ad copy. Google takes some liberties with what they display in search results, so your meta description may not always show, but if you have a compelling description of your page that would make folks searching likely to click, you can greatly increase traffic. (Remember: showing up in search results is just the first step! You still need to get searchers to come to your site, and then actually take the action you want.)
QUOTE: “Duplicated content is often not manipulative and is commonplace on many websites and often free from malicious intent. Copied content can often be penalised algorithmically or manually. Duplicate content is not penalised, but this is often not an optimal set-up for pages, either. Be VERY careful ‘spinning’ ‘copied’ text to make it unique!” Shaun Anderson, Hobo, 2018
Brian Dean, an SEO expert and the creator of BackLinko, uses SEO tactics to rank #1 on YouTube for keywords like “on page SEO” and “video SEO”. Initially, Dean admits his YouTube account struggled to get any views. Employing SEO methods like keyword optimization has enabled Dean to rise to #1 on YouTube for search results related to his business. He published his full strategy on Backlinko.
If you want to *ENSURE* your FULL title tag shows in the desktop UK version of Google SERPs, stick to a shorter title of between 55-65 characters but that does not mean your title tag MUST end at 55 characters and remember your mobile visitors see a longer title (in the UK, in January 2018). What you see displayed in SERPs depends on the characters you use. In 2019 – I just expect what Google displays to change – so I don’t obsess about what Google is doing in terms of display. See the tests later on in this article.

Google WILL classify your site when it crawls and indexes your site – and this classification can have a DRASTIC effect on your rankings. It’s important for Google to work out WHAT YOUR ULTIMATE INTENT IS – do you want to be classified as a thin affiliate site made ‘just for Google’, a domain holding page or a small business website with a real purpose? Ensure you don’t confuse Google in any way by being explicit with all the signals you can – to show on your website you are a real business, and your INTENT is genuine – and even more important today – FOCUSED ON SATISFYING A VISITOR.
All too often, people dramatically overthink the most basic keyword research concepts; keyword generation should start simply with answering the question of "What products or services do you sell?" If you sell dog food online,  the root words dog and food alone would be very poor keywords because on their own, neither dog nor food do a remotely good job at describing what you sell. Though this example makes it obvious, many times we have to fight through our urge to include those bigger, broader root keywords.
At my comapny, Wpromote, we use this tool to help shape overall content strategies. Continuing with the dog food example, we can see that ratings, comparison, and reviews all were all grouped as closely related to dog food in general, implying that people that are searching for dog food are very interested in the comparison and review side of things. So from a content strategy perspective, it would be a very powerful takeaway to include a heavy emphasis on customer ratings, third-party reviews, and side by side comparisons to help the consumers make their dog food selections while shopping on our site.
However, we do expect websites of large companies and organizations to put a great deal of effort into creating a good user experience on their website, including having helpful SC. For large websites, SC may be one of the primary ways that users explore the website and find MC, and a lack of helpful SC on large websites with a lot of content may be a reason for a Low rating.
When Googlebot crawls a page, it should see the page the same way an average user does15. For optimal rendering and indexing, always allow Googlebot access to the JavaScript, CSS, and image files used by your website. If your site's robots.txt file disallows crawling of these assets, it directly harms how well our algorithms render and index your content. This can result in suboptimal rankings.