SEO, Social Media, etc are basics that everybody knows nowadays.
I am nowhere close to my goal but nevertheless, I get around 300-400 unique visitors every day, 70%-80% from Google search, and I earn enough to live without a full-time job. That is because as a travel blogger I have taken the effort to visit many obscure places that no one else is covering. So, once I write about them, I start ranking more often than not (as no one else has covered them). I am not writing about cliched tourist spots, or the same done to death topics (like how to quit your job to travel the world and such extreme cliches).
So, ultimately you must think of something in your field, that nobody (or at least not too many) are writing about. Something that is new but at least some people are looking for. A new blog can't just compete with scores of existing sites and rank high on google immediately unless you have something unique. And yes, ultimately the primary source will have to be organic search traffic. In social media, you will have to keep posting every day (and even your friends will get tired if you post too much) but once you rank in google, they will come to you themselves.
It is, of course, a long process so don't get disheartened immediately. At least for the first year or so don't think too much about earning. Focus on the content. They will come.