There are currently approximately 250 main ranking signals in Google's algorithm and the better you address each and every one of these signals, the more successful you'll be. Each of these signals can be placed onto five pillars (with content marketing being the foundation). Here's the link to an article I wrote about our "5 Pillars of SEO" methodology and here's the link to an article I wrote about international SEO best practices. This should give you a good idea on how to get started.
It really depends on a ton of factors (short- or long-tail keywords, competitors SEO efforts, etc.). However, once we start to deploy an SEO campaign for our clients, we usually see results within 3-4 months.