As a healer main, level a tank job and do as many different dungeons as possible.

As a tank main, level a healer job and do as many different dungeons as possible.

This will help you understand what the other role can and cannot do, as well as get yourself familiarized with specific cool downs, play styles, and capabilities of the other role. This will also allow you to make better decisions about the capability of the other role because you now understand the nuances of the role.