I usually use Emergency Tactics as a sort of "backup" Indomitability after really big hits (like the 24-man raid-wide attacks that puts everyone at really low health). Usually it goes: attack hits > Indomitability > Emergency Tactics > Succor. If the other healer pops at least one AoE heal as well, that puts mostly everyone at full health.
Dissipation is only really useful as a DPS tool (use it during the start of a fight to freely blow three Energy Drains on the boss) or during real emergencies where you really need an Aetherflow stack for Lustrate/Indomitability. I don't use it much, really, but it can be handy.
Indomitability is best used right after big hits, if everyone is stacked up. It has a pretty short range, unfortunately. If you don't have many stacks and have to choose between Sacred Soil before the hit and Indomitability after the hit, Indomitability is usually the way to go since it's a rather strong heal (for a SCH anyway, it still pales in comparison to Cure III). As I said above, save your stacks for when you need them, but if you still have stacks when Aetherflow's cooldown is nearly finished, just blow the remaining stacks on Energy Drains so you get extra MP.
