Today I asked myself a question - how soon it takes to rank on Google?

Based on my experience it could be in average 3-6 month. But I decided to Google this question, and read what other might said, and found a really useful article, where it's simple explained - How long does it take a website to rank on Google? 

What I liked the most - Fat head, chunky middle and long tail:

Go and read that article, which will guide you through content building methods for better SEO. Don't focus just on Fat head keywords, chunky middle, and long tail will give you the most at start.

So by doing chunky middle and long tail articles, your SERP will go up.