Building links is an art. It's almost certainly the most challenging part of an SEO's job, and, for many sites, the one most critical to achieving long term success. Many companies can afford to hire SEOs to help make their websites search friendly and search optimized, but a robust backlink profile is an extremely high barrier to competition.
As with any marketing activity, the first process undertaken in a link building campaign must be the creation of goals and strategies. Sadly, link building is one of the most difficult activities to measure, particularly from a search engine optimization perspective. Although the engines internally weight each link precise, mathematical metrics, it's impossible for those outside of the engineering team at these companies to extract this data. Thus, as SEOs, we rely on a number
of signals to help build a rating scale of link value.