Google, in many instances, would rather send long-tail search traffic, like users using mobile VOICE SEARCH, for instance, to high-quality pages ABOUT a concept/topic that explains relationships and connections between relevant sub-topics FIRST, rather than to only send that traffic to low-quality pages just because they have the exact phrase on the page.
QUOTE: “We do use it for ranking, but it’s not the most critical part of a page. So it’s not worthwhile filling it with keywords to hope that it works that way. In general, we try to recognise when a title tag is stuffed with keywords because that’s also a bad user experience for users in the search results. If they’re looking to understand what these pages are about and they just see a jumble of keywords, then that doesn’t really help.” John Mueller, Google 2016

QUOTE: “I think that’s always an option. Yeah. That’s something that–I’ve seen sites do that across the board,not specifically for blogs, but for content in general, where they would regularly go through all of their content and see, well, this content doesn’t get any clicks, or everyone who goes there kind of runs off screaming.” John Mueller, Google 
But essentially the idea there is that this is a good representative of the the content from your website and that’s all that we would show to users on the other hand if someone is specifically looking for let’s say dental bridges in Dublin then we’d be able to show the appropriate clinic that you have on your website that matches that a little bit better so we’d know dental bridges is something that you have a lot on your website and Dublin is something that’s unique to this specific page so we’d be able to pull that out and to show that to the user like that so from a pure content duplication point of view that’s not really something I totally worry about.

Websites that have extremely negative or malicious reputations. Also use the Lowest rating for violations of the Google Webmaster Quality Guidelines. Finally, Lowest+ may be used both for pages with many low-quality characteristics and for pages whose lack of a single Page Quality characteristic makes you question the true purpose of the page. Important: Negative reputation is sufficient reason to give a page a Low quality rating. Evidence of truly malicious or fraudulent behavior warrants the Lowest rating.
You can confer some of your site's reputation to another site when your site links to it. Sometimes users can take advantage of this by adding links to their own site in your comment sections or message boards. Or sometimes you might mention a site in a negative way and don't want to confer any of your reputation upon it. For example, imagine that you're writing a blog post on the topic of comment spamming and you want to call out a site that recently comment spammed your blog. You want to warn others of the site, so you include the link to it in your content; however, you certainly don't want to give the site some of your reputation from your link. This would be a good time to use nofollow.
QUOTE: “Medium pages achieve their purpose and have neither high nor low expertise, authoritativeness, and trustworthiness. However, Medium pages lack the characteristics that would support a higher quality rating. Occasionally, you will find a page with a mix of high and low quality characteristics. In those cases, the best page quality rating may be Medium.” Google Quality Evaluator Guidelines, 2017
Sometimes, Google turns up the dial on demands on ‘quality’, and if your site falls short, a website traffic crunch is assured. Some sites invite problems ignoring Google’s ‘rules’ and some sites inadvertently introduce technical problems to their site after the date of a major algorithm update and are then impacted negatively by later refreshes of the algorithm.
I’ve always thought if you are serious about ranking – do so with ORIGINAL COPY. It’s clear – search engines reward good content it hasn’t found before. It indexes it blisteringly fast, for a start (within a second, if your website isn’t penalised!). So – make sure each of your pages has enough text content you have written specifically for that page – and you won’t need to jump through hoops to get it ranking.
Many blogging software packages automatically nofollow user comments, but those that don't can most likely be manually edited to do this. This advice also goes for other areas of your site that may involve user-generated content, such as guest books, forums, shout-boards, referrer listings, etc. If you're willing to vouch for links added by third parties (for example, if a commenter is trusted on your site), then there's no need to use nofollow on links; however, linking to sites that Google considers spammy can affect the reputation of your own site. The Webmaster Help Center has more tips on avoiding comment spam40, for example by using CAPTCHAs and turning on comment moderation.
The biggest advantage any one provider has over another is experience and resource. The knowledge of what doesn’t work and what will hurt your site is often more valuable than knowing what will give you a short-lived boost. Getting to the top of Google is a relatively simple process. One that is constantly in change. Professional SEO is more a collection of skills, methods and techniques. It is more a way of doing things, than a one-size-fits-all magic trick.

Another excellent guide is Google’s “Search Engine Optimization Starter Guide.” This is a free PDF download that covers basic tips that Google provides to its own employees on how to get listed. You’ll find it here. Also well worth checking out is Moz’s “Beginner’s Guide To SEO,” which you’ll find here, and the SEO Success Pyramid from Small Business Search Marketing.