Wikipedia probably receives more traffic from Google than any other website. With over 2 million in depth articles the English version is most people's idea of a perfectly optimised site so what can we learn from it?
The first points are all on-page factors. Looking at the site we can see that the pages all have search engine friendly file names, title tags and meta descriptions as well as mainly text based content. This is very important when you compare Wiki articles against normal e-commerce pages with very little text based content.
The final and one of the most important on page factors is the internal linking between documents. Notice that every time an article mentions the title of another article it is turned into a text link? This plays a huge part in improving the sites rankings.
The off-site factors are fairly simple. Wikipedia has been branded as a free site that offers a huge amount of (usually) high quality information. This means that millions of websites deep link to different articles giving the site an unrivalled trusted status in the eyes of Google.
Lessons to be learned from Wikipedia are straightforward: structure your site and article pages in the same way and fill your site with truly interesting and useful content.
The actual implementation of this strategy is easier said than done but it is still surprising how many e-commerce sites get this part totally wrong.