SEO ranking factors is a topic I am interested in from quite some time now. The reason for this is that I am a web developer and i also manage a few websites, incl apersonal blog.
There are more than a few hundred ranking factors that have impact on SEO. Luckily for us, not all of them are equal.
From my experience and also from what i have studied so far, some of the most important factors include:
1. Writing unique, high quality content, long articles. Google tends to favour informative and concise posts and put them in the front because this is what users want after all.
2. Having high quality back links from reputable websites give your website page authority. That is the way to validate your website in the internet.
3. Meta tags such as title, description, etc. are still important. However, these tags are not "everything", as they used to be a few years ago. As far as i know, Google does not look at the keywords tags anymore, though the title tag is still very impotant. The image alt tag is also important seo factor.
This is to give you some insights but you should keep in mind that SEO is a whole science, so i cannot wrap it up in one post :)
I hope this helps!