Google page rank algorithm is based on this formula
PR(A) = (1-d) + d (PR(T1)/C(T1) + ... + PR(Tn)/C(Tn))
PR(A) is the PageRank of page A,
PR(Ti) is the PageRank of pages Ti which link to page A,
C(Ti) is the number of outbound links on page Ti and
d is a damping factor which can be set between 0 and 1.
So, first of all, we see that PageRank does not rank web sites as a whole, but is determined for each page individually. Further, the PageRank of page A is recursively defined by the PageRanks of those pages which link to page A.
To increase the page rank you have to continuously work on the site. Have to build the site with quality contents and back links. Since they are very essential for search engine optimization.
Page rank is all about the quality (page rank) of pages linking to any given page. You can build a high PR on a page within your site while having a low PR on your landing page, though high PR children share rank with parents.
you can increase your PR buy optimizing your site build backlinks as well as improve your traffic
I agree with it. I want to add one more thing in it. Content optimization is very important factor to gather good page rank. I have different experience with my website. There are 76 web pages in my website and I am working on home page with my link building campaign. I never approach or start link building for inner pages but inner pages have very good page rank. (1 to 4 page rank) I assumed that it's due to unique content and started work on unique content plus proper content optimization. Now, I can see some hike in page rank for inner pages after edition of content with unique one.
Google doesn't set any criteria to your website page rank it's totally depends on your qualitative work, how to you optimize your website using best SEO,SMO Link building tactics, but remember Google always change their algorithms.