Backlinks, which go from other websites back to your website, are the foundation of off-site search engine optimization. Not all backlinks are created equal, however. As you build backlinks, here's how to evaluate their usefulness for your offsite-SEO.
Authority of Site
The authority of a website transfers to the authority of its links. In other words, well-known websites with established reputations provide links that are ranked better by search engines.
Major news publications and universities often have extremely authoritative sites, but websites like these can be difficult to get links from. Simply look for the most respected sites that you can get links from.
Age of Site
The age of a website often impacts its authority. Websites become more established and thus more authoritative over time. While not a universal rule, links from older sites have more worth than those from new sites. This is especially true when comparing newer websites, which often aren't well established.
Type of Link
Backlinks are classified as either do-follow links or no-follow links. Do-follow links to your website boost the importance of your linked page. No-follow links don't actually transfer authority in search engine algorithms.
Most off-site SEO efforts focus on obtaining do-follow links because these are what algorithms calculate authority by. No-follow links still are important, though, because having several of them shows that your site is naturally growing.
Correlation of Subject
How closely the content on a backlinking website correlates to the content of your website influences how much weight a link is given. Assuming two sites have the same authority, the one that's directly related to your niche will have more weight than one that's outside of your niche.
For example, assume you're conducting off-site SEO for a website that helps visitors find colleges that are suitable for them. A link from an education blog will have more import than a link from a website that's about children's toys.
Location of Link
Not all of the links on a page are given equal weight, and the difference between the most important ones and the least important ones can be substantial. While it's impossible to calculate the exact difference in how important two links on the same page are, a couple of guidelines will help with general evaluation.
First, a link within the content is better than one that's not directly in the content. For instance, a link that occurs within the main body of a blog post is considered better than one that's in a sidebar or footer.
Second, links that are higher on a page are generally weighed more than those that occur lower down on a page.