Keep resources crawlable. Blocking page resources can give Google an incomplete picture of your website. This often happens when your robots.txt file is blocking access to some or all of your page resources. If Googlebot doesn't have access to a page's resources, such as CSS, JavaScript, or images, we may not detect that it's built to display and work well on a mobile browser. In other words, we may not detect that the page is "mobile-friendly," and therefore not properly serve it to mobile searchers.
When would this be useful? If your site has a blog with public commenting turned on, links within those comments could pass your reputation to pages that you may not be comfortable vouching for. Blog comment areas on pages are highly susceptible to comment spam. Nofollowing these user-added links ensures that you're not giving your page's hard-earned reputation to a spammy site.
In 2013, the Tenth Circuit Court of Appeals held in, Inc. v. 1-800 Contacts, Inc. that online contact lens seller did not commit trademark infringement when it purchased search advertisements using competitor 1-800 Contacts' federally registered 1800 CONTACTS trademark as a keyword. In August 2016, the Federal Trade Commission filed an administrative complaint against 1-800 Contacts alleging, among other things, that its trademark enforcement practices in the search engine marketing space have unreasonably restrained competition in violation of the FTC Act. 1-800 Contacts has denied all wrongdoing and is scheduled to appear before an FTC administrative law judge in April 2017.[29]
Sharing Curated Links — While using social media for marketing is a great way to leverage your own unique, original content to gain followers, fans, and devotees, it’s also an opportunity to link to outside articles as well. If other sources provide great, valuable information you think your target audience will enjoy, don’t be shy about linking to them. Curating and linking to outside sources improves trust and reliability, and you may even get some links in return.
Social media can be used not only as public relations and direct marketing tools but also as communication channels targeting very specific audiences with social media influencers and social media personalities and as effective customer engagement tools.[15] Technologies predating social media, such as broadcast TV and newspapers can also provide advertisers with a fairly targeted audience, given that an ad placed during a sports game broadcast or in the sports section of a newspaper is likely to be read by sports fans. However, social media websites can target niche markets even more precisely. Using digital tools such as Google Adsense, advertisers can target their ads to very specific demographics, such as people who are interested in social entrepreneurship, political activism associated with a particular political party, or video gaming. Google Adsense does this by looking for keywords in social media user's online posts and comments. It would be hard for a TV station or paper-based newspaper to provide ads that are this targeted (though not impossible, as can be seen with "special issue" sections on niche issues, which newspapers can use to sell targeted ads).
In addition to giving you insight into the search volume and competition level of keywords, most keyword research tools will also give you detailed information about the average or current estimated CPC for particular keywords are. This is particularly important for businesses with smaller ad budgets and this feature allows you to predict whether certain keywords will be truly beneficial to your ad campaigns or if they’ll cost too much.
Search engine marketing (SEM) is a form of Internet marketing that involves the promotion of websites by increasing their visibility in search engine results pages (SERPs) primarily through paid advertising.[1] SEM may incorporate search engine optimization (SEO), which adjusts or rewrites website content and site architecture to achieve a higher ranking in search engine results pages to enhance pay per click (PPC) listings.[2]

You should build a website to benefit your users, and any optimization should be geared toward making the user experience better. One of those users is a search engine, which helps other users discover your content. Search Engine Optimization is about helping search engines understand and present content. Your site may be smaller or larger than our example site and offer vastly different content, but the optimization topics we discuss below should apply to sites of all sizes and types. We hope our guide gives you some fresh ideas on how to improve your website, and we'd love to hear your questions, feedback, and success stories in the Google Webmaster Help Forum1.

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.
Page and Brin founded Google in 1998.[23] Google attracted a loyal following among the growing number of Internet users, who liked its simple design.[24] Off-page factors (such as PageRank and hyperlink analysis) were considered as well as on-page factors (such as keyword frequency, meta tags, headings, links and site structure) to enable Google to avoid the kind of manipulation seen in search engines that only considered on-page factors for their rankings. Although PageRank was more difficult to game, webmasters had already developed link building tools and schemes to influence the Inktomi search engine, and these methods proved similarly applicable to gaming PageRank. Many sites focused on exchanging, buying, and selling links, often on a massive scale. Some of these schemes, or link farms, involved the creation of thousands of sites for the sole purpose of link spamming.[25]