Eye-tracking studies can be extremely revealing about how your users are using your site in the real world. Unfortunately, they can also be extremely expensive and time-consuming to conduct. Not everyone in charge of a website has those kind of resources.
Luckily for us, some organizations have made some of their information public, giving us the chance to do gain some insights about our own pages.
Also, Prioritizing Web Usability by Hoa Loranger and Jakob Nielsen provides a good amount of data gathered from eye-tracking studies, among a plethora of other valuable insights.