This guide made healing much easier as Sage:

A few key points.

Always have Kardia on the tank.
Always use physis/krasia on tank before using mitigation. (alternate Taurochole and Karochole as they will overwrite each other and this is a waste)
Keep sheilds up on tank while pulling. You can hear the beep or ding when the shield has been broken indicating youve receive a stack of addergall, then reapply shield.
Dont forget about Soteria and Zoe to buff your shields.

Theres a lot more, I highly recommend watching this through its entirety.

https://www.youtube.com/watch?v=UPjdwUgwncI&t=142s