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.

QUOTE: “Search engine optimization 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.” Google Starter Guide, 2008
Robots.txt is not an appropriate or effective way of blocking sensitive or confidential material. It only instructs well-behaved crawlers that the pages are not for them, but it does not prevent your server from delivering those pages to a browser that requests them. One reason is that search engines could still reference the URLs you block (showing just the URL, no title or snippet) if there happen to be links to those URLs somewhere on the Internet (like referrer logs). Also, non-compliant or rogue search engines that don't acknowledge the Robots Exclusion Standard could disobey the instructions of your robots.txt. Finally, a curious user could examine the directories or subdirectories in your robots.txt file and guess the URL of the content that you don't want seen.
“Doorways are sites or pages created to rank highly for specific search queries. They are bad for users because they can lead to multiple similar pages in user search results, where each result ends up taking the user to essentially the same destination. They can also lead users to intermediate pages that are not as useful as the final destination.
The reality in 2019 is that if Google classifies your duplicate content as THIN content, or MANIPULATIVE BOILER-PLATE or NEAR DUPLICATE ‘SPUN’ content, then you probably DO have a severe problem that violates Google’s website performance recommendations and this ‘violation’ will need ‘cleaned’ up – if – of course – you intend to rank high in Google.
Optimizing a website may involve editing its content, adding content, and modifying HTML and associated coding to both increase its relevance to specific keywords and remove barriers to the indexing activities of search engines like Google ,Yahoo etc.[citation needed] Promoting a site to increase the number of backlinks, or inbound links, is another SEO tactic. By May 2015, mobile search had surpassed desktop search.[3]
The basics of GOOD SEO hasn’t changed for years – though effectiveness of particular elements has certainly narrowed or changed in type of usefulness – you should still be focusing on building a simple site using VERY simple SEO best practices – don’t sweat the small stuff, while all-the-time paying attention to the important stuff  – add plenty of unique PAGE TITLES and plenty of new ORIGINAL CONTENT. Understand how Google SEES your website. CRAWL it, like Google does, with (for example) Screaming Frog SEO spider, and fix malformed links or things that result in server errors (500), broken links (400+) and unnecessary redirects (300+). Each page you want in Google should serve a 200 OK header message.
When referring to the homepage, a trailing slash after the hostname is optional since it leads to the same content ("" is the same as ""). For the path and filename, a trailing slash would be seen as a different URL (signaling either a file or a directory), for example, "" is not the same as "".
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.
Another reason is that if you're using an image as a link, the alt text for that image will be treated similarly to the anchor text of a text link. However, we don't recommend using too many images for links in your site's navigation when text links could serve the same purpose. Lastly, optimizing your image filenames and alt text makes it easier for image search projects like Google Image Search to better understand your images.
Users will occasionally come to a page that doesn't exist on your site, either by following a broken link or typing in the wrong URL. Having a custom 404 page30 that kindly guides users back to a working page on your site can greatly improve a user's experience. Your 404 page should probably have a link back to your root page and could also provide links to popular or related content on your site. You can use Google Search Console to find the sources of URLs causing "not found" errors31.
Another illicit practice is to place "doorway" pages loaded with keywords on the client's site somewhere. The SEO promises this will make the page more relevant for more queries. This is inherently false since individual pages are rarely relevant for a wide range of keywords. More insidious, however, is that these doorway pages often contain hidden links to the SEO's other clients as well. Such doorway pages drain away the link popularity of a site and route it to the SEO and its other clients, which may include sites with unsavory or illegal content.
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.
Being ‘relevant’ comes down to keywords & key phrases – in domain names, URLs, Title Elements, the number of times they are repeated in text on the page, text in image alt tags, rich markup and importantly in keyword links to the page in question. If you are relying on manipulating hidden elements on a page to do well in Google, you’ll probably trigger spam filters. If it is ‘hidden’ in on-page elements – beware relying on it too much to improve your rankings.
SEO is also about making your search engine result relevant to the user's search query so more people click the result when it is shown in search. In this process, snippets of text and meta data are optimized to ensure your snippet of information is appealing in the context of the search query to obtain a high CTR (click through rate) from search results.