Link building is the key for an effective SEO campaign. This works best for PR and SERP. Always provide useful and relevant content in your websites niche as this will help in quality organic linking - sites will naturally link to your site once they see unique and helpful information in your site. Keep in mind that the more targeted backlinks you build for your site, the more likely it will bring in the right visitors that could make the conversions for better revenue. You do targeted link buidling for fast and long term traffic to your sites.