In SEO Part II: Links, we discussed the importance of incoming links from high-ranking sites in the same area as yours. What other factors influence the value of incoming links?
Aside from relative popularity, some sites are considered by Google to be particularly authoritative; Wikipedia is one example, but there are others. Pages on Wikipedia can outrank pages on other sites that have a lot more useful information, due to the site’s importance. A vote from these “expert sites” is thus worth more than most. You can read more about this by Googling ‘Hilltop Algorithm’.
Other good sites to get backlinks from are those with .edu or .gov TLDs. While these pages don’t actually get a pagerank boost (at least, so says Google), they do tend to be considered more authoritative, so backlinks from them increase Google’s estimation of your site’s trustworthiness.
The value of links from web directories varies; generally you want to get links from human-created directories that are well organized and link to other good sites, while avoiding those that are automatically created. Of course, you’ll also want to check that the links aren’t using the nofollow attribute, so they pass along link juice.
As previously mentioned, it’s helpful to be one of just a few links rather than one of thousands, so as to get the largest possible share of link juice. Also, remember that Google considers content closer to the top of the page to be more important; thus, it’s good if your link shows up close to the beginning of the HTML file (which is not the same as showing up at the top of the page when displayed – see the note on CSS in that last link!)
It can be discouraging to go to a lot of effort getting new links without seeing a corresponding increase in your pagerank, but remember that, like sites, links need to “age”; a backlink that’s been around for a while is worth a lot more than a new link that could be gone tomorrow. Slowly building links over time tends to lead to a gradual increase in the pagerank of your site. But be sure to read part five about when pagerank doesn’t matter!