Druid is the most self sufficient healer. Innervate is considerably more powerful than Mana Tide for the individual target. The key issue with druids is the ramp up mentality required for it. Our weakness, and our strength, start to show during phases of heavy group damage. When you are required to switch targets frequently, our mastery loses a great deal of its value and going into AoE healing mode there is sort of a ramp up as a Druid. Burning the Tree of Life cooldown however greatly reduces the burden of switching into an AoE healing mode. Once we've started getting HoTs out on all the targets, such as Tree of Life's lifebloom blanketing mode, we are a very effective party or raid healer. However fights don't always have heavy AoE damage, it tends to come in phases (for example, on Omnitron I only ever use Tree of Life on Magmatron, and the cooldown matches the spawning cycle perfectly). Once you get a second HoT on targets your ramp up is complete and you can heal that target more effectively. Casting Wild Growth prior to blanketing Rejvenations in a 5 man for instance is effective. Casting Wild Growth means that your Rejuvenation will benefit from Mastery. Then when Wild Growth is off cooldown, recast it and it will benefit from Mastery since Rejuvenation is on all the targets. Druid healing is always more effective if you can land multiple spells on your target that requires healing. In Tree of Life you would simply cycle Wild Growth and with Lifebloom instead, only using Rejuvenation if you need a Swiftmend (or the Effloresence of it for healing a cluster of people).
The key concept of being an effective Druid healer is getting that second heal on the target (unless damage is so small that it isn't necessary).
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.