Duels 

Invest in duels and make sure you can survive (as a healer) or crush all 10 classes.
Work on your weak spots the most.
Use duels as a way to find those blind/weak spots.

For example, if you discover you cannot beat a rogue, or survive a rogue, then ask one to talk you through what they are doing to crush you, and learn from it. Learn the icons that appear for their abilities, and learn their cooldowns. Learn to work around them.