Provide full functionality on all devices. Mobile users expect the same functionality - such as commenting and check-out - and content on mobile as well as on all other devices that your website supports. In addition to textual content, make sure that all important images and videos are embedded and accessible on mobile devices. For search engines, provide all structured data and other metadata - such as titles, descriptions, link-elements, and other meta-tags - on all versions of the pages.
The world is mobile today. Most people are searching on Google using a mobile device. The desktop version of a site might be difficult to view and use on a mobile device. As a result, having a mobile ready site is critical to your online presence. In fact, starting in late 2016, Google has begun experiments to primarily use the mobile version of a site's content42 for ranking, parsing structured data, and generating snippets.
When Googlebot crawls a page, it should see the page the same way an average user does15. For optimal rendering and indexing, always allow Googlebot access to the JavaScript, CSS, and image files used by your website. If your site's robots.txt file disallows crawling of these assets, it directly harms how well our algorithms render and index your content. This can result in suboptimal rankings.
Website saturation and popularity, or how much presence a website has on search engines, can be analyzed through the number of pages of the site that are indexed by search engines (saturation) and how many backlinks the site has (popularity). It requires pages to contain keywords people are looking for and ensure that they rank high enough in search engine rankings. Most search engines include some form of link popularity in their ranking algorithms. The following are major tools measuring various aspects of saturation and link popularity: Link Popularity, Top 10 Google Analysis, and Marketleap's Link Popularity and Search Engine Saturation.

Let’s say, for example, that you run a construction business that helps with home repairs after natural disasters and you want to advertise that service. The official term for the service is “fire restoration,” but keyword research may indicate that customers in your area search instead for “fire repair” or “repair fire damage to house.” By not optimizing for these two keywords, you’ll lose out on a lot of traffic and potential customers, even if “fire restoration” is technically more correct.
Optimization techniques are highly tuned to the dominant search engines in the target market. The search engines' market shares vary from market to market, as does competition. In 2003, Danny Sullivan stated that Google represented about 75% of all searches.[64] In markets outside the United States, Google's share is often larger, and Google remains the dominant search engine worldwide as of 2007.[65] As of 2006, Google had an 85–90% market share in Germany.[66] While there were hundreds of SEO firms in the US at that time, there were only about five in Germany.[66] As of June 2008, the market share of Google in the UK was close to 90% according to Hitwise.[67] That market share is achieved in a number of countries.
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.[22] 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.
In 2007, U.S. advertisers spent US $24.6 billion on search engine marketing.[3] In Q2 2015, Google (73.7%) and the Yahoo/Bing (26.3%) partnership accounted for almost 100% of U.S. search engine spend.[4] As of 2006, SEM was growing much faster than traditional advertising and even other channels of online marketing.[5] Managing search campaigns is either done directly with the SEM vendor or through an SEM tool provider. It may also be self-serve or through an advertising agency. As of October 2016, Google leads the global search engine market with a market share of 89.3%. Bing comes second with a market share of 4.36%, Yahoo comes third with a market share of 3.3%, and Chinese search engine Baidu is fourth globally with a share of about 0.68%.[6]
Google's search engine marketing is one of the western world's marketing leaders, while its search engine marketing is its biggest source of profit.[17] Google's search engine providers are clearly ahead of the Yahoo and Bing network. The display of unknown search results is free, while advertisers are willing to pay for each click of the ad in the sponsored search results.

Optimizing a website may involve editing its content, adding content, modifying HTML, and associated coding to both increase its relevance to specific keywords and to remove barriers to the indexing activities of search engines.[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]