Here are a few ways that Search Engines judge the value of a link:
1. Internal vs. External: a link from an external domain is more valuable than internal links.
2. Anchor Text: an anchor text will pass more relevancy/ranking value if it’s an “exact match” keyword (e.g. local search engine optimization services vs. Big Leap’s local search engine optimization services really helped me out). The first one is the best choice.
3. Content links: links from the content of a page are more valuable than a link from a resources page or just a list of links.
4. Trust Rank: get links from trusted sites, and never link to potential spam sites. If you get links from trusted sites, Google will be more likely to trust your site in return.
5. Diversity of sources: earning a link from a site that’s already linked to you in the past is not as valuable as getting a link from an entirely unique domain.