Swiftcast your biggest heal for those osnap situations for tanks

Swiftcast your biggest group heal for those massive damage spikes to the group (espically if your not good at precasting)

Not much else I can think of doing for a WHM. For a SCH you can do the following:

Swiftcast Eos/Selene

Swiftcast Shadow Flare

Our 20% HP heal is already instant cast, so thats all I can really think of.