As you know the healing class is the Druid's restoration specialization. At higher levels, specializing will significantly decrease your tanking (bear) and damage-per-second (cat) abilities. While you can still transform, your power in these shapes will be significantly decreased without the talents in the feral tree. Still, restoration Druids are some of the most efficient healers in the game, having quick Heal-over-Time spells which are excellent for arena and Player vs. Player and the Tree Form, which is a great benefit in raiding parties.
   For restoration Druid, there are lots of talent builds but all of them focus on filling the restoration talent tree for the most part. Even some feel that you need not spend the full amount of points necessary to gain access to the tree of Life form, restoration Druids are the most powerful when completely specialized.
   Since most of your power will come from your Heal over Time spells, it is best to ignore spending points on Healing Touch talents like Naturalist, Tranquil Spirit, and Empowered Touch. Instead, maximize the talents that increase your other spells such as Improved Regeneration, Gift of Nature, Improved Regrowth, and Empowered Rejuvenation.
   It is a must to spend points on Swiftmend which gives you the Swiftmend spell will instantly turn a Heal over Time spell already cast into an instant heal. For your longer duration spells such as Regrowth and Rejuvenation, this spell can often restore more hit points than a Priest's most powerful heals. Plus, as an instant cast, this is wonderful for getting the tank out of a tight spot and preventing a wipe.
   It is useful to make use of extra points in the Feral tree as a boost to getting out of difficult situations whereas it is better to spend points in the Balance tree. In particular, Nature's Grasp is useful as a way to get an instant Entangling Roots put on a rogue without having to spend time casting the spell. Control of Nature also helps to avoid interruption when casting some of your more powerful Heal-Over-Time spells.
   Given that restoration Druids are the most useful for casting a number of Heal-Over-Time Spells and maintaining a party's overall hit points. However, you must take more notice of everyone and make sure that your tank always has Heal over Time on him. It is very difficult for restoration Druids to heal players whose heals is almost gone if they are still in combat as heals take longer to work with the exception of using Swiftmend.
   You can sometimes keep track of which players do not have Heal over Time on them any longer. Mods like Damage over Time timer are quite useful for giving you a graphical of which Heal over Times you have in play.
   Make sure that your Entangling Roots and Cyclone spells are useful in arenas. Use Cyclone on healers, DPS casters whereas Entangling Roots on Rogues, Warriors. Also, remember that you can cast Hibernate to put a hunter's pet to sleep.
   If you get into trouble, casting Nature's Grasp to root a melee class attacking you is a great defense. Plus, if you are in further danger or running out of mana, switch to travel form and run away from the combat to quickly heal yourself or restore mana.
Try to save your Innervate spell for when you are running low on mana. Casting this spell on yourself when you have about 20% left is usually best if you have decent Spirit.
   At length, you do not forget your party buffs: Gift of the Wild and Thorns which are small bonuses, but they add up when granted to your entire party.