Today we're talking about how search engines value links!
External vs Internal
External links tend to be more valuable than internal links. Search engines look at external links like a vote in favor of a site. That external vote from another site is something that search engines are going to take far more seriously than an internal link. They're going to value it much more highly in terms of the editorial value.
Authority
Links from more important and authoritative sites are going to tend to be of higher value than links from sites that are less important. They don't look like they have as many links as mine. Well, it could very well be the case that their links come from more important sources than yours do.
Link Freshness
Links from sites that haven't linked to you before tend to be more valuable than links from sites that already have link pointing at your domain. If a site has already linked to me once a second link that comes in from another page on their site would not be as valuable as a link from another site.
Link Diversity
Links from sites owned by unique entities tend to be more valuable than sites owned by the same company. For example, if a network of blog sites owned by the same entity links to each other doesn’t seem very diversified. Google and Bing are going to know that those are the same entity and aren’t going to be treated as truly external and unique sites.
Anchor Text Relevancy
Links that contain anchor text related keywords that you're targeting may help you rank better for those specific terms and phrases. If you've got a link from the Seattle Times to Plaid Shirts Rule and that link says "plaid shirts," in the anchor text. It is probably going to help you rank better for this precise phrase. That anchor text in the link is something that search engines value pretty highly.
Footers and Sidebars
Links from a page's content or body text will pass more value than links from a footer or sidebar. The best possible place for me to get a link is in the content, because that's where the article or the editorial authority is coming from. Links from sidebars or footers are associated with advertising, promotions, or sponsorships, which don’t pass much authority.
Spam
Links from site that have too many spammy or manipulative links may be devalued. You might have a beautiful link from the Seattle Times, but if they are not paying attention to what's going with their site and lots of spammers are posting links to the same page it could hurt your SEO. Search engines devalue links from spammy pages.
Higher Authority Pages
Links from a page has a good external and internal link profile pass more value. If a Seattle Times article performs particularly well a link from this article will pass more value than lesser linked to pages. That's often why some SEO folks will say, "hey, I got a great link from an article on this news site. I'm going to link to that site from other places or try and do some actually link earning to that page to help the value that it's driving."
Too Many Links
Links on pages with many other links, and I don't mean many like 100. I mean many hundreds of links. It's likely that with those they may pass less value because there are so many links already on that page, and essentially the link dilution is happening there. It's essentially not passing as much value out.