Numerous academic papers concerning PageRank have been published since Page and Brin's original paper.[5] In practice, the PageRank concept may be vulnerable to manipulation. Research has been conducted into identifying falsely influenced PageRank rankings. The goal is to find an effective means of ignoring links from documents with falsely influenced PageRank.[6]

The Open Directory Project (ODP) is a Web directory maintained by a large staff of volunteers. Each volunteer oversees a category, and together volunteers list and categorize Web sites into a huge, comprehensive directory. Because a real person evaluates and categorizes each page within the directory, search engines like Google use the ODP as a database for search results. Getting a site listed on the ODP often means it will show up on Google.
Collaborative Environment: A collaborative environment can be set up between the organization, the technology service provider, and the digital agencies to optimize effort, resource sharing, reusability and communications.[36] Additionally, organizations are inviting their customers to help them better understand how to service them. This source of data is called User Generated Content. Much of this is acquired via company websites where the organization invites people to share ideas that are then evaluated by other users of the site. The most popular ideas are evaluated and implemented in some form. Using this method of acquiring data and developing new products can foster the organizations relationship with their customer as well as spawn ideas that would otherwise be overlooked. UGC is low-cost advertising as it is directly from the consumers and can save advertising costs for the organisation.
A lot of folks aim their ads at the broadest possible terms, such as “dresses,” or “bike parts,” or “search engine optimization.” Since the broader terms get far more searches, it’s a strong temptation – with a big disadvantage. Since everyone bids on the broad terms, the cost per click is generally quite high. And the chances of a conversion, even if someone clicks on your ad, are lower.
The overall rule of thumb? Focus, focus, focus. Organic search engine optimization is a PR-based, long-term attempt to grow your brand and image. Pay per click advertising, however, should be handled like any other form of paid advertising: proactively, and with a clear, quantifiable short- or medium-term goal in mind. In other words: concentrate on conversions, not just clicks.

In February 2011, Google announced the Panda update, which penalizes websites containing content duplicated from other websites and sources. Historically websites have copied content from one another and benefited in search engine rankings by engaging in this practice. However Google implemented a new system which punishes sites whose content is not unique.[35] The 2012 Google Penguin attempted to penalize websites that used manipulative techniques to improve their rankings on the search engine.[36] Although Google Penguin has been presented as an algorithm aimed at fighting web spam, it really focuses on spammy links[37] by gauging the quality of the sites the links are coming from. The 2013 Google Hummingbird update featured an algorithm change designed to improve Google's natural language processing and semantic understanding of web pages. Hummingbird's language processing system falls under the newly recognised term of 'Conversational Search' where the system pays more attention to each word in the query in order to better match the pages to the meaning of the query rather than a few words [38]. With regards to the changes made to search engine optimization, for content publishers and writers, Hummingbird is intended to resolve issues by getting rid of irrelevant content and spam, allowing Google to produce high-quality content and rely on them to be 'trusted' authors.
To put it simply, a SERP is a page full of possible answers that follow a query entered into a search engine. To digital marketers, SERPs are golden real estate opportunities for generating high volume traffic. In order to capitalize on those opportunities, marketers must understand the Google search page layout and how to utilize the appropriate listings to the highest visibility. 
Secondly, nofollow is also essential on links to off-topic pages, whether they’re internal or external to your site. You want to prevent search engines from misunderstanding what your pages are about. Linking relevant pages together reinforces your topic relevance. So to keep your topic silos clear, strategic use of the nofollow attribute can be applied when linking off-topic pages together.
Google has a very large team of search quality raters that evaluate the quality of search results, that gets fed into a machine learning algorithm. Google’s search quality rater guidelines provide plenty of detail and examples of what Google class as high or low quality content and websites, and their emphasis on wanting to reward sites that clearly show their expertise, authority and trust (EAT).

In 1998, two graduate students at Stanford University, Larry Page and Sergey Brin, developed "Backrub", a search engine that relied on a mathematical algorithm to rate the prominence of web pages. The number calculated by the algorithm, PageRank, is a function of the quantity and strength of inbound links.[21] PageRank estimates the likelihood that a given page will be reached by a web user who randomly surfs the web, and follows links from one page to another. In effect, this means that some links are stronger than others, as a higher PageRank page is more likely to be reached by the random web surfer.