Druids in World of Warcraft are a "Jack of all trades". They can fill the multiple class roles on the fly, and excel at specific aspects of multiple classes directly. To decide on a specific aspect to focus on, consider the three Talent trees available to Druids:
Each talent tree focuses on different aspects of the game and how the Druid applies themselves to situations in both solo and group play. As a Balance Druid, you specialize in Mage-like casting typically with the ability to off-heal in emergency situations. As a Feral Druid, you specialize in Melee type combat with either Rogue-like DPS abilities or Warrior-like Tanking abilities. As a Restoration Druid, you specialize in restorative group healing with unique nature spells.
While the above holds true for PvE content, PvP will create new hurdles to overcome and bend the specifics of each talent tree to work best in player vs player encounters. Balance Druids in PvP typically fit the role of dangerous survivability casters with respectable armor and casting DPS in a mobile state. Feral Druids in PvP fit the role of terribly hard to kill melee monsters but do not tend to be as popular as Balance or Restoration due to the lack of survivability with low Mana pools and healing/casting stats. Restoration Druids in PvP tend to be the most popular choice due to their ability to create extremely mobile, elusive, and effective HoT healers that are hard to trap and kill.
Druid healing has two popular and viable points of interest. One is Tree of Life (ToL) healing, which grants very strong HoT (Heal over Time) bonuses and the other is what's been titled "Dreamstate" healing which is a Hybrid build between Balance and Restoration that focuses on MP5 (Mana regen in-combat) and the use of Healing Touch effectively.
This base build includes necessities such as Intensity for MP5, Nature's Swiftness, Swiftmend, and Tree of Life while providing as much of a bonus to HoT-based spells such as Regrowth and Rejuvenation. Lifebloom, a unique HoT introduced with TBC expansion, does not have any directly associated talents at this time and is directly affected by Idols (Relic) and Bonus Healing stat. Typically, omitting one point from Improved Regrowth is in no way damaging to the build if you decide to go 41/20 to get 4 full tiers in your off-spec Talent Tree.
As a Restoration Druid, the idea of playing solo for farming and daily quest purposes comes into question. "How does one farm" you might ask? Well, a viable off-spec is where to start! With a similar Restoration build similar to what's outlined above, you have the choice of either using Balance or Feral as an off-spec. Both have their advantages and disadvantages, so the decision is primarily based on what you enjoy the most. Let's start with a Balance off-spec.
Balance is a very viable choice for Restoration Druids as an off-spec due to Blizzards change that made the Bonus Healing stat have weight in determining the Bonus Damage stat. This means that this off-spec is great for people that don't like to carry around multiple full gear sets in their inventory at all times. Your Bonus Healing will translate into a percentage of Bonus Damage by default and therefore make soloing fairly easy. As an example, a fairly effective Balance off-spec includes:
This build lets you effectively deal moderate caster DPS damage while having effective snaring abilities (ie. Root Casting). Your Wrath casting speed is decreased for faster DPS output and you have a chance to stun with Starlight spell casts. You also get increased range and Insect Swarm, which added to Moonfire and Entangling Roots creates a very effective DoT effect. This focuses on the most basic aspects of the Balance tree while maintaining all the essentials from Restoration
Feral is a viable choice for Restoration Druids as an off-spec if you enjoy getting up close and personal with melee DPS, while having the cunning of a Rogue with stealth abilities or the brawn of a Warrior with tank abilities. This typically requires an additional gear set to carry around with you (or bank while you're not using it), and offers a completely different solo/farming experience for the Druid. As an example, a fairly effective Feral off-spec includes:
This build lets you effectively deal good melee DPS damage while adding some bonuses like Feral Swiftness or Feral Charge. If you prefer the Rogue-like Cat Form, you will probably omit Feral Charge and take the full 2 points in Feral Swiftness. If you prefer Bear, you will enjoy the charge stun Feral Charge provides while still having some increased mobility in Cat Form with one point in Feral Swiftness.