Mega-sites, like have tens or hundreds of editors writing new content – i.e. new pages - all day long! Each one of those pages has rich, worthwile content of its own and a link back to its parent or the home page! That’s why the Home page Toolbar PR of these sites is 9/10 and the rest of us just get pushed lower and lower by comparison…

All sites have a home or "root" page, which is usually the most frequented page on the site and the starting place of navigation for many visitors. Unless your site has only a handful of pages, you should think about how visitors will go from a general page (your root page) to a page containing more specific content. Do you have enough pages around a specific topic area that it would make sense to create a page describing these related pages (for example, root page -> related topic listing -> specific topic)? Do you have hundreds of different products that need to be classified under multiple category and subcategory pages?
In this illustration from the “PageRank Citation Ranking” paper, the authors demonstrate how webpages pass value onto other pages. The two pages on the left have a value of 100 and 9, respectively. The page with a value of 100 has two links that point to the pages on the right. That page’s value of 100 is divided between the two links, so that each conveys a value of 50. The other page on the left has three outgoing links, each carrying one-third of the page’s value of 9. One link goes to the top page on the right, which ends up with a total value of 53. The bottom right page has no other backlinks, so its total value is 50.
Imagine that you've created the definitive Web site on a subject -- we'll use skydiving as an example. Your site is so new that it's not even listed on any SERPs yet, so your first step is to submit your site to search engines like Google and Yahoo. The Web pages on your skydiving site include useful information, exciting photographs and helpful links guiding visitors to other resources. Even with the best information about skydiving on the Web, your site may not crack the top page of results on major search engines. When people search for the term "skydiving," they could end up going to inferior Web sites because yours isn't in the top results.
One thing is certain: interlinking sites doesn't help you from a search engine standpoint. The only reason you may want to interlink your sites in the first place might be to provide your visitors with extra resources to visit. In this case, it would probably be okay to provide visitors with a link to another of your websites, but try to keep many instances of linking to the same IP address to a bare minimum. One or two links on a page here and there probably won't hurt you.
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).
According to the U.S. Commerce Department, consumers spent $453.46 billion on the web for retail purchases in 2017, a 16.0% increase compared with $390.99 billion in 2016. That’s the highest growth rate since 2011, when online sales grew 17.5% over 2010. Forrester predicts that online sales will account for 17% of all US retail sales by 2022. And digital advertising is also growing strongly; According to Strategy Analytics, in 2017 digital advertising was up 12%, accounting for approximately 38% of overall spending on advertising, or $207.44 billion.

Such an enlightening post! Thanks for revealing those sources, Brian. This really has opened up my mind to the new ideas. I have read many articles about SEO, especially the ones in my country, most of them don’t really tell how to increase your presence in search engines. But today I found this page, which gave me much more valuable insights. Definitely going to try your tips..

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