Hi, A site back link can increase ,when your site PR will be more and more ,because low PR site add High PR site link on its Links page to get PR on there site but they add only relevant site...So try to make your page Excellent in view of google ...
I hate to say this, but Web sites don't have PageRanks. Only Web pages do. Every single page on a Web site has its own PageRank value - whether it's the actual PR that Google keeps to itself and factors into the search results, or the toolbar PageRank value that gets pushed out to the public every quarter - makes no difference whatsoever. Not only that, but when a page with a low PageRank adds a link to a page with a high PageRank, that low PR page is essentially "voting" for the high PR page, which means the high PR page is the one that will benefit the most. Now, if you were to reverse the roles by having the high PR page link to the low PR page, then the low PR page would have the advantage - especially if the two pages were related to each other (in other words, relevant). And if you want to have a great site in Googles' eyes, try to make it as easy to find, easy to access and easy to use as possible. One of the things I've always told people (and Google has pretty much made this their "standard answer" from the looks of things) is to forget about the search engines when building a Web site and developing its content. Instead, put the focus on the people who will be using it. If you can do that (make the site accessible, easy to use, and have a good document structure and information architecture) while putting your users first, chances are that Google and the other search engines will give you that "preferential treatment" you're seeking.