- The link should be mutually beneficial.
- The link should make logical sense.
P.S. I am writing this a week after the original post to add a great resource. I just sat through a webinar presented by WordTracker on link building. The presenter, Ken McGaffin, was fantastic. He covers the subject thoroughly and the hour flew by. He is, of course, demonstrating their Link Builder software, but the information is valuable whether you use their software or not. I intend to take it for a trial run!