I think by now, most of the principles of SEO are more or less well understood by people that have done their time in the trenches since 1999, although new platforms and data types arrive all the time keeping the need for ongoing practice or testing even more important than in the past. The need to learn about new entrants like Siri, Alexa, Facebook, Linkedin, and specialist search engines (like Booking.com, for example) will keep SEOs on their toes for years to come.
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.

Structured data21 is code that you can add to your sites' pages to describe your content to search engines, so they can better understand what's on your pages. Search engines can use this understanding to display your content in useful (and eye-catching!) ways in search results. That, in turn, can help you attract just the right kind of customers for your business.
Facebook had an estimated 144.27 million views in 2016, approximately 12.9 million per month.[109] Despite this high volume of traffic, very little has been done to protect the millions of users who log on to Facebook and other social media platforms each month. President Barack Obama tried to work with the Federal Trade Commission (FTC) to attempt to regulate data mining. He proposed the Privacy Bill of Rights, which would protect the average user from having their private information downloaded and shared with third party companies. The proposed laws would give the consumer more control over what information companies can collect.[107] President Obama was unable to pass most of these laws through congress, and it is unsure what President Trump will do with regards to social media marketing ethics.
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.
SEO is also about making your search engine result relevant to the user's search query so more people click the result when it is shown in search. In this process, snippets of text and meta data are optimized to ensure your snippet of information is appealing in the context of the search query to obtain a high CTR (click through rate) from search results.
Inbound marketing refers to a marketing methodology wherein you attract, engage, and delight customers at every stage of the buyer's journey. You can use every digital marketing tactic listed above, throughout an inbound marketing strategy, to create a customer experience that works with the customer, not against them. Here are some classic examples of inbound marketing versus traditional marketing: 
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