Popularity and Relevancy. These two concepts make up the bulk of Search Engine Optimization theory. The way they are determined and the relationship between them changes, but they are both fundamental to determining search results.
THE SECRETS OF POPULARITY
RELEVANCE, SPEED, AND SCALABILITY
Hypothetically, the most relevant search engine would have a team of experts on every subject in the entire world—a staff large enough to read, study, and evaluate every document published on the web so they could return the most accurate results for each query submitted by users.
The fastest search engine, on the other hand, would crawl a new URL the very second it's published and introduce it into the general index immediately, available to appear in query results only seconds after it goes live.
The challenge for Google and all other engines is to find the balance between those two scenarios: To combine rapid crawling and indexing with a relevance algorithm that can be instantly applied to new content. In other words, they're trying to build scalable relevance. With very few exceptions, Google is uninterested in hand-removing (or hand-promoting) specific content. Instead, its model is built around identifying characteristics in web content that indicate the content is especially relevant or irrelevant, so that content all across the web with those same characteristics can be similarly promoted or demoted.
Google's focus on creating relevant, user-focused content really is the key to its algorithm of scalable relevance. Google is constantly trying to find ways to reward content that truly answers users' questions and ways to minimize or filter out content built for content's sake.
Although a webmaster can easily manipulate everything (word choice, keyword placement, internal links, and so on) on his or her own website, it is much more difficult to influence inbound links. This natural link profile acts as an extremely good metric for identifying legitimately popular pages.
Domain and Page Popularity
There are hundreds of factors that help engines decide how to rank a page. And in general, those hundreds of factors can be broken into two categories—relevance and popularity (or "authority"). For the purposes of this demonstration you will need to completely ignore relevancy for a second. (Kind of like the search engine Ask.com.) Further, within the category of popularity, there are two primary types—domain popularity and page popularity. Modern search engines rank pages by a combination of these two kinds of popularity metrics. These metrics are measurements of link profiles. To rank number one for a given query you need to have the highest amount of total popularity on the Internet.
Although en.wikipedia.org has a lot of domain popularity and get.adobe.com/reader/ has a lot of page popularity, www.awesome.com ranks higher because it has a higher total amount of popularity. This fact and relevancy metrics are the essence of Search Engine Optimization.
In my opinion, hyperlinks are the most important factor when it comes to ranking web pages. This is the result of them being difficult to manipulate. Modern search engines look at link profiles from many different perspectives and use those relationships to determine rank. The takeaway for you is that time spent earning links is time well spent. In the same way that a rising tide raises all ships, popular domains raise all pages. Likewise, popular pages raise the given domain metrics.
THE SECRETS OF RELEVANCY
Text is the Currency of the Internet
Relevancy is the measurement of the theoretical distance between two corresponding items with regards to relationship. Luckily for Google and Microsoft, modern-day computers are quite good at calculating this measurement for text. So what does this emphasis on textual content mean for SEOs? To me, it indicates that my time is better spent optimizing text than images or videos. This strategy will likely have to change in the future as computers get more powerful and energy efficient, but for right now text should be every SEO's primary focus.
But Why Content?The search engines must use their analysis of content as their primary indication of relevancy for determining rankings for a given search query. For SEOs, this means the content on a given page is essential for manipulating—that is, earning—rankings. In the old days of AltaVista and other search engines, SEOs would just need to write "Jessica Simpson" hundreds times on the site to make it rank #1 for that query. What could be more relevant for the query "Jessica Simpson" than a page that says Jessica Simpson 100 times? (Clever SEOs will realize the answer is a page that says "Jessica Simpson" 101 times.) This metric, called keyword density, was quickly manipulated, and the search engines of the time diluted the power of this metric on rankings until it became almost useless.
Similar dilution has happened to the keywords meta tag, some kinds of internal links, and H1 tags.
In addition to the words on a page, search engines use signals like image meta information (alt attribute), link profile and site architecture, and information hierarchy to determine how relevant a given page that mentions "Jessica" is to a search query for "The Simpsons."
As search engines matured, they started identifying more metrics for determining rankings. One that stood out among the rest was link relevancy.
The difference between link relevancy and link popularity (discussed in the previous section) is that link relevancy does not take into account the power of the link. Instead, it is a natural phenomenon that works when people link out to other content.
People have a tendency to link to content using the anchor text of either the domain name or the title of the page. Use this to your advantage by including keywords you want to rank for in these two elements.
Other important relevancy indicators are link sources and information hierarchy. For example, the search engines can also use the fact that I linked to the color choice article from a blog about whiteboard markers to supplement their understanding of relevancy.
Similarly, they can use the fact that the original article was located at the URL www.example.com/vision/color/ to determine the high-level positioning and relevancy of the content.
Beyond specific anchor text, proximal text—the certain number of characters preceding and following the link itself—have some value.
Something that's logical, but annoying is when people use a verb as anchor text, such as "Frank said …" or "Jennifer wrote …", using "said" or "wrote" as the anchor text pointing back to the post. In a situation like that, engines have figured out how to apply the context of the surrounding copy to the link.