Twelve Metrics That Search Engines Consider For Ranking

There are dozens of answers to this question, but some of the most relevant and important would be:

* Anchor text (when it matches queries, it can have a significant positive impact)
* Placement on the page
* PageRank of the linking page (more PR = more good)
* Trust in the linking domain (more trust = ++)
* Link structure in HTML (inside an image, javascript, standard a href, etc.) - although Javascript links are sometimes followed, they appear to provide only a fraction of the link weight that normal links grant. Likewise, links from images (and anchor text in the form of alt text) appears to provide somewhat less weight than standard HTML links.
* Temporal nature of the link (when it appeared, how long it stays on the page for, etc.) - can affect how much weight the link is given and be used to identify patterns that may indicate manipulation
* Use of nofollow
* Relevance of page content to linked-to page (more relevant = better)
* Relevance of site to linked-to page (more relevance = better)
* Text surrounding the link (as the two above)
* Previous link relationships between the domains (if the page/site has already linked to the page/site in the past, it may be given less weight and this may also be used to identify and discount reciprocal linking schemes)
* Hosting relationships (if the domains are hosted on the same IP address, or same c-block of IP addresses, the link may lose some of its weight)
* Registration relationships (if the domains share registration information, it may be interpreted as less editorial and given less weight)