For the most part, if you die, the rest of the group will go along with you, even more so than the tank dying. There is something innate in someone playing the healer role that wants to make sure your save other even if that is to sacrifice yourself. You have to learn (and trust) that the tank can take care of him/herself for that 2-3 seconds while you heal yourself.

Positioning:
Another important lesson to learn is positioning. Start to train your eyes to not just looking at the health bars of others but the big picture. Pay attention of what's going on. You will need to when you start to get to the 8-players fights as a lot of AoE can one shot a healer if you don't pay attention. Again, like the triage situation, you need to save yourself first. If someone is low on HP, you are casting a Cure II but an AoE circles pops underneath you, move immediately, no question ask. It will be very tempting to finish the cast, but the risk is too high.