Links are very important in any sort of SEO campaign in the digital age. Getting links usually consumes most of the budget and time in effective SEO strategies. While onsite optimization is done fairly fast, link building is costly, takes time and involves a lot of hard work.
Link building involves a lot of common sense. This is because the most worthwhile and powerful links come from established and relevant sites, which are hard to find. As you search for these sites remember ‘no-follow’ and ‘follow’ links. Google came up with ‘no-follow’ links to allow linking without going through PR (page rank).
Theoretically, no follow links seem to offer any value but it does not mean they should be avoided. Natural building of links is what Google looks out for, a process incorporating no-follow links and thus both follow and no-follow links must be mixed. Focus on getting follow links as much as possible, but do not exclude no-follow links.
As you build links, remember search engines respect naturally built links. It is not easy to define the natural nature of the process but avoid seeking links from irrelevant sites, which also link to other non-related sites. Obviously, you will be punished for buying links.
The recent Panda and Penguin updates by Google have changed the terrain of link building in the digital age and you must be careful to avoid the Google punishment as well as being blacklisted by other search engines. The truth is that only Google engineers understand the quantification and measurement of the most valued links. Avoid quick fixes and use some logic.