Well. Its not a big matter at all. Its mostly about building back links from high PR sources. Its the formula for calculating a site's PR
PR(A) = (1-d) + d (PR(T1)/C(T1) + ... + PR(Tn)/C(Tn))
Where,
D- damping factor considered as 0 to 1
A - Site to be found PR
T1 - Site from where the link is coming from
C - OBL's of T1.
And Somebody says, Without even a single Link, we can get PR upto 2 by posting unique and useful contents in our site. This will drive certain number of unique visitors to our site daily.
And, some other says, number of indexed pages in a site is involved in calculating the Page Rank of a site. For example, n number of pages of a site are indexed, it has certain number of PR.
Anyway, It would be good top get faster PR, if we concentrate on both of those three techniques. We just can't leave any technique as everything is must to keep.
Just my opinions. If anything i need to correct, please let me know. I'm looking for someone to let me know it completely.