Incoming links are one of the most important factors for high search engine rankings. If your website doesn't have enough incoming links then it's very difficult to get high rankings for a competitive search term.
It's important that you get the right kind of links. If you have 20 good incoming links then you'll get better rankings than with 100 bad incoming links.
So what makes a good incoming link? There are several points that can make a link better than other links: