Page Rank.

Page Rank is link analysis algorithm used by Google engines. Page rank determine relative importance of a link within their database. Google Re-evaluate page rank 3 to 4 times per year, so for almost every 4 months Google calculate your page rank. 
How to increase Page Ranking?

1. Link Building:

 Link building is a process of acquiring backlinks from other websites to your website.

2. High quality 

content and update content: The website should be updated in a manner that benefits the users and show Google that the website is fresh and deserves higher ranking. 

3. Site submit on Search Engine:

 Site submission refers to submission of a website to a search engine. It is the effective way of web promotion. 

4. Guest posting:

 Guest posting means to post the content and URL of a website on another site.

5. Link Exchange and Directory submission:

 Link exchange helps to build a relationship between the websites and an increase in link popularity results in increase in page ranking.

6.Directory submission

 is a common SEO technique to get back links for the submitted website