There is strong evidence that PageRank is the MAIN factor that gives a webite's positioning in the results pages. To increase your PageRank, you should get as many external links as possible pointing to your homepage. The links should be from pages with high PageRanks. It seems that a link from a website with PageRank ZERO (most of the time link pages are ZERO PageRank, you can check that, in the link page you know!!) is worth 200 times (!!!) less than a link from a page with PageRank TWO or THREE. You can get increase Page Rank by exchanging link with similar Page Rank pages and can get next higher Page Rank. So it better to exchange link with home page (first page) with same Page Rank.
Other impotent factor is that if your link is located among lots of links (as example in a link page among 100s link) it is less chance you get improvement in your PageRank with that link. So it is always better to get link from home page or 'early' pages.
Problem is that most of the times you can not get same field web page to exchange. Nobody like to put text link of irrelevant web page in you home or main page and give the bad impression to visitors.
But you can do it carefully by placing links some places avoiding your visitor’s eye directly. (selecting less visible places in your web pages)
These links are text link that place in less important corner in your main page. Visitors cannot see them directly. (Remember visitor spend only few second in a web page if they are not really reading) These are not hidden link or ‘illegal’ links as any careful eye can see them.
You can request link exchange with 'Google rank' pages . You get more links of same PageRank and provides same link to others. You have to mention the PageRank you want and ready to provide link in same PageRank web page.