(1) Links to your site that have been around awhile have more value than new ones.
(2) Links from reputable sources (with high PageRank) have more value than from poorly ranked sites.
(3) Links from sites that are relevant to your site have more value than, say, a link from a site about lipstick to a site about the manufacture of pistons for cars.
(4) At the same time, many links from different addresses (IP’s) have more value than a few from one or a few addresses and diversity of anchor text is better than a single anchor text repeated.
Peter Rubel
