2) After reading above, you will automatically ignore most of the BS that passes as 'strategy' and 'advice' about (digital) marketing on the internet. Everyone's a guru- most gurus couldn't sell something effectively online if their lives depended on it.
3)Learn copywriting from Direct Mail marketers. Same principles apply. Technology changes- human behaviour, needs, wants, insecurities rarely do.
4) Understand that the consumer doesn't give a shit about you or your brand. They're not 'brand evangelists', 'advocates'. 'Engagement' doesn't mean anything if it doesn't lead to sales. If they have a problem, and you solve it, they'll tolerate you or give you the appropriate amount of attention. Then they'll move on with their lives. Don't get caught up in metrics that don't affect your bottom line.
5) Points 1-4 don't matter if you don't set up your own site and start selling something. Period. If you have your own time, energy and resources invested into making digital marketing work, you will learn more by necessity than you ever would by reading Quora, digital marketing blogs, taking online courses, etc.