I’ve been studying SEO deliberately and methodically for about a year now (after many years of studying it accidentally and haphazardly). Most of what I’ve learned can be boiled down to this 5-year-old gem from Matt Gemmell:
“Good SEO is a by-product of not being a dick on the internet.”
Or, the slightly more informative version:
“Stop being a dick on the internet. Write something interesting, and keep doing it for months and years. SEO will then follow naturally.”
Of course this is not quite the whole story about SEO. It would be a little more accurate to say that good SEO is mainly a by-product of not being a dick on the Internet, plus a light sauce of knowledge about metadata and how Googlebot works. (There’s nothing obvious about the power of alt tags, for instance: you have to grok why they matter to an algorithm.) To some extent, SEO always involves a little bit of pandering to that very special non-human reader.