Backlinks building is one of the most important ways to increase the page rank of your site. The higher your page rank, the more often your site will appear on the top searches results. Linkbuilding means linking to the other sites by inbound links. The higher the page rank of the sites that you are linked to, the higher Google or any other SEO will rank your site. It is also important that the content where you are linked to is similar to the subject of your site. If, for example your site is about the sport cars it is senseless to be linked to the site about the gardening. Also try to link to the sites with the high page rank, such links will influence more on the page rank of your own site.