Link building is a fundamental part of search engine optimisation but, of course, not all links are equal. Determining link quality is an important skill as although no link to your site will have a negative effect on your ranking, a good link can be worth a thousand poor links and some links will have no benefit at all.

Some of the factors that affect link quality are:

* PageRank
* Content Relevancy
* Anchor Text
* Number Of Links On Page

There are other factors that come into play, such as link position on page, but the above factors will make the biggest difference to a link’s benefit. It is also worth noting that by "quality" I am really talking about a link’s contribution to search engine optimisation efforts and its ability to improve listings. A link can be considered extremely valuable if it sends a steady stream of traffic to your site, but this is not the focus of this post.

Of the above factors, relevancy is the most important. It is common for people to place too much emphasis on the importance of PageRank. Whilst high PR links are desirable, a link from page with no PageRank at all can still be beneficial. To illustrate this point, it is worth considering that while a page’s relevancy is unlikely to change, its PageRank may improve significantly within a few months.

If you receive a link request from a relevant company who has placed your link on a PR 0 page, do not dismiss it immediately. It may be on a quality page that is just new but will be given a much higher PR at the next update. Alternatively, it may be on one of a hundred links pages that is not cached by the search engines.

The number of links on the page is an important factor because the PageRank that is "passed" from the links page will be shared among all of the links whether internal or external. With all other things being equal, a page with a PR 4 and 5 links will provide a greater benefit than a PR 5 with 50 links.

Anchor text is important because it will help your site rank for specific terms. For example, Adobe ranks first in Google for the term "click here" because of the huge number of sites that use phrases such as "click here to download adobe reader" to like to Adobe. Link anchor text to your site should include keywords where possible. It is best to vary anchor text and use specific terms rather than generic words.

As an additional note, while inbound links will not harm your site, outbound links can. For that reason, be very careful of accepting reciprocal link exchanges from sites that use link farms, black hat techniques or that belong to "bad neighbourhoods".