Since I used to play a Healer before the Burning Crusade and I raided as one for most of BC, I get some questions on how to heal in Northrend. While I agree with most that it is much harder to heal in Lich King compared to BC and could be one of the reasons why we do not see as many healers in Lich King.
For Druids the best way to heal is based on a rotation system just like it is as DPS as a Moonkin. Tanks love Druids now because their HoTs are more powerful than they used to be and now can be considered Tank healers with the right rotation. The best rotation is this, while you need to use Regrowth as well during some periods, this is something you should follow.
Rejuv > Lifebloom > Lifebloom > Lifebloom > Wild Growth
With that rotation you are putting all your HoTs on your Tank and on top of that you are healing your raid at the same time. If the Tank is losing too much health, too fast try this rotation instead:
Regrowth > Lifebloom > Lifebloom > Lifebloom > Rejuv > Swiftmend >Wild Growth
This is where you need Direct Heals more so than HoTs. Rejuv goes last as it will works with Swiftmend. By the time you use Wild Growth and Regrowth again Swiftmend should be ready to use again. While this rotation uses more Mana than the first rotation, it is best used if you are going to be a tank healer when you do not have a Priest or Paladin to help you out.
If you are going to be raid healers like Druids were in BC, than the following rotation will work. Note that this applies to each member in your group.
Rejuv > Lifebloom > Wild Growth
Now with the 6 second cool down, you need to learn how to space Wild Growth’s time limit. If you are a raid healer you can also just use Wild Growth and then wait 6 seconds, but you would not be a good raid healer with that. This is why the best rotation is the first rotation and make sure you tell your raid leader that you want to be a Tank healer, either MT or OT.