Alright, here's a bare-bones guide to Nature healing.
Metabolism, Savage Growth, Blossom, Regeneration
Swarm Shield, Hive Mind
Different situations in which you use your powers:
1. For small heals (ie. topping off people's health), use Savage Growth and/or Metabolism.
2. For big heals (ie. spike damage, tank healing), cast Savage Growth, clip with Metabolism then cast Blossom. Savage Growth + Metabolism + Blossom heals more than Metabolism + Blossom or Savage Growth + Blossom.
3. For emergency heals (ie. everyone low on health), use your supercharge, Regeneration.
4. For a bonus to healing and dps, use Hive Mind.
5. For a damage-prevention shield for your party and to avoid spike damage, use Swarm Shield.
Basic power rotation for boss fight
1. If you have Swarm Shield, cast Swarm Shield before fight starts.
2. When fight starts, cast Savage Growth and/or Metabolism.
3. Wait a few seconds to see how combat progresses. If there's a big dip in someone's health, cast Blossom for a big heal. Otherwise, if incoming damage is low, you may want to continue waiting or cast another Metabolism/Savage Growth for a heal-over-time.
4. Refresh your Savage Growth and/or Metabolism once their cooldowns are up.
5. If you have surplus power (more than half your power remaining), cast Swarm Shield if its not on cooldown.
6. Repeat steps 3-5 till combat ends.
Note: You may want to use Regeneration for emergency heals and Hive Mind in conjunction with trinket for an extra healing boost.
TLDR - Just spam Savage Growth, clip with Metabolism, followed by Blossom, repeat ad-infinitum.
Enjoy your romp as a Nature healer!