Understanding how links work
Link Prioritisation can be looked upon as a system for optimising your linking structure throughout your site to pass the maximum page rank to your important pages and to separate any pages you don’t want to be indexed, crawled, or a combination of both. Using things like the rel="nofollow" attribute on links stops valuable page rank being passed across to those linked pages. Think about this simple example; you have a page with a high page rank and it links to various other pages on your site, obviously this page only has a certain amount page rank it can pass to each of the linked pages, and if any of these pages are not important to your site you should block them with a rel=" nofollow". Before you attempt to do this, please try to grasp the concept behind this, it isn’t about manipulating your linking structure, or blocking off good content pages that you don’t think are important, it’s about sealing off useless pages or pages that could lead to duplicate content problems, such as pages with random URL parameters, shopping cart pages and various information pages that don’t need to show in search results.
Optimise your linking structure
If you completely optimise your linking structure you should have all your content pages easily accessible from each other both for users and search engines and you should have blocked off useless pages on your site that you don’t want indexed. While a robots text file can be used to block off directories and pages, you can use the rel="nofollow" attribute on links to block those pages at a page level. It’s all about prioritising links in the eyes of search engines and is a key factor in creating a well optimised site in terms of SEO. If you want to put this concept into practice go though the links within one of your pages one by one and have a look and think is it pointless having a search engine crawler bot follow this link.
Blocking external links
You can also have a look at blocking external links, an example of this is if you take card payments on your website and have a link to a card provider (a lot of sites usually do down the bottom of a page), you can safely place a rel="nofollow" on these links, as there is no way linking back to these generic unrelated sites will benefit you, the page rank is much better being passed to pages within your own site. You shouldn’t go mad and just place a rel=" nofollow" on every external link, the natural development of the internet and page rank depends on website placing links to each other that pass page rank as a vote of confidence in each other. If you link to an external site and you think it should be passed page rank then by all means do.