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.
Trust is the foundation of conversions and sales. But building trust should be a goal on its own. The whole concept of content marketing is based on trust and creating long-term relationships. Stop selling and let the people come to you by providing them interesting and useful information. I couldn’t have said it better than Mark Schaefer, the Executive Director of Schaefer Marketing Solutions:
Tablet - We consider tablets as devices in their own class, so when we speak of mobile devices, we generally do not include tablets in the definition. Tablets tend to have larger screens, which means that, unless you offer tablet-optimized content, you can assume that users expect to see your site as it would look on a desktop browser rather than on a smartphone browser.