Important skills are discussed here in alphabetical order.
Abolish Disease
At level 32 this skill becomes available as a replacement for Cure Disease. For 40 mana more than Cure Disease, it abolishes 1 disease every 5 seconds for 20 seconds. Once this becomes available, this should be your main method of curing diseases.
Blackout
Stuns are very strong in World of Warcraft. They allow you time to recover, time to get off some damage, or time to heal yourself. More importantly for PvP, they confuse the enemy. Few people expect to be stunned by a priest at range. PvP is where this talent shines, and is essential. The stun coming at an opportune moment can turn the tide of battle your way.

Blessed Recovery
A good talent on paper that is unfortunately let down in practice. The way the heal is calculated makes this talent sub-par. The amount to be healed depends on the most recent critical hit, rather than the highest, so huge crits can be overwritten by smaller ones. This is especially noticable against rogues, who crit often, with large and small amounts.
Cure Disease
Use this skill until abolish disease is available. It’s generally best to save your mana for heals when in groups, unless it is a disease that causes damage or drains mana. Wait until after the battle to removes diseases. It’s up to your discretion whether to cure a disease mid battle.
Darkness
Unlike Shadow Weaving, this is a passive skill, and does not require activation and cannot be dispelled. It is a great boost to damage and any Shadow specced priest who has spent the points to access this far down the tree should take this talent.
Dispel Magic
This is a fantastic spell for PvP and a useful spell in some PvE situations. Unless you are being ganked, you should begin every fight with a dispel magic. All the armour increasing spells are dispel able, as are health and mana buffs. Potion effects are also dispel able. Against most classes you will need to cast this twice to remove all the buffs. This can also be used to remove SW:Pain when fighting priests and a number of Warlock DoT’s. It can also remove the negative effects of a Shaman’s shocks. Dispel magic now checks that a target can be dispelled before expending any mana, which has made it even more powerful.
Divine Fury

This is quite a useful talent for those spending points past the first tier. It affects both healing and the damage dealing role of a priest, so it gets bonus points there. Additionally, it helps in an area that holy priests usually suffer; dealing damage. It also makes Greater Heal a 2.5 second cast, making it extremely useful as a main healing spell.

Divine Spirit
This is an average spell, which has been improved by its new position in the talent tree. It synergises well with other priest talents also. It is always nice to have an extra buff available to give to your party. extra points of Spirit.
Fade
Fade is an essential spell in any group situation. At higher levels, elite mobs can plow through your health in seconds. This removes a set amount of agro, hopefully enabling the tank to resume his role. How Fade works in regards to agro reduction is complicated, and will be explained in another section. This is a spell that should be on any healer’s hotbar.
Flash Heal
Flash heal is a fast casting, medium healing spell. It is less mana efficient than Greater Heal, but can be more effective in situations where damage fluctuates. In the end game raid instances, Flash Heal will be your primary healing spell in most situations, combined with Renew. Critical hits and monster damage at that level is so high that tanks can die before a Greater Heal can be accomplished. You should also use this heal on any other cloth wearers in your group.

Force of Will
Force of will is a good talent for soloing Discipline-heavy priests, but not really worth the talent investment. If it were lower down the tree it would be more useful, but having it so high means that it costs at least 30 talent points to be able to max it, talents which could be better spent elsewhere. If you really need a damage boost and have no where else to spend the points, get it. Otherwise, ignore it.
Greater Heal
Greater Heal has a long cast time but heals for a large amount. It is also affected by more talents than Flash Heal. With all talents applied, Greater Heal is the most mana efficient heal, assuming no healing is wasted. With the recent talent changes, Greater Heal has become a lot more attractive as a main healing spell. It now has a 3 second base cast time, which can be further reduced to 2.5 seconds with talents. It is now possible to use this as a primary heal, combined mainly with Renew to keep a tank topped up.
Heal
Heal, Lesser Heal and Greater Heal all have the same mana efficiency in terms of health per mana point, so they are essentially the same spell. Once Greater Heal is available at level 40, Heal becomes obsolete.
Healing Focus
This is one of the best talents in the game, and should be taken by any priest regardless of what their role will be. It costs only 2 talent points, is situated on the first tier, and is a huge boost to effectiveness. Brilliant in both PvE and PvP. A must have talent.
Holy Fire
Holy Fire no longer requires a point in the Holy tree, and thus is a stronger spell. It has a long casting time (which can be reduced with talents). As the damage is split between an initial burst, then a DoT element over ten seconds, it is more effective as an opener than when used constantly. Use this when pulling in PvE, and in some PvP builds with certain specs and gear.
Holy Nova

Holy Nova is more a fun spell to spam than a useful talent point. The best element of this spell is that it creates no threat, which means it can be used with impunity in situations where mana is not a concern (such as the Vael fight). It can also be useful in battlegrounds, where it is sometimes difficult to use your mana before dying.

Holy Reach
Talents that increase range are generally considered essential in most builds. Holy Reach is not essential in the sense that Shadow Reach is, but it is still a nice talent to have. If you plan on doing any PvP as a Holy priest, you should definitely consider this talent. Otherwise, it becomes less attractive.
Holy Specialization
Combined with a bonus from Intellect, this should take your critical chance to around 10%. This is another good talent situated so low in the tree, but is overshadowed by its rival Improved Renew + Healing Focus. Critical heals can be lifesavers, but are generally too unreliable to be useful, and in most cases the extra healing will go to waste. It is more effective to those who like to use Flash Heal over Greater Heal, because the criticals have more chance of healing for the full amount. Healing crits have been fixed recently, making this a more viable talent, but still underwhelming.
Inner Fire
The best armour buff spell in the game in terms of damage reduction. This should more than double your base armour, which can be helpful for paper-thin priests. The spell now lasts 10 minutes, but comes with a rather limited 20 charges. The armour value of each level has been increased, making it a stronger spell on a whole, with a slight down side.
Inner Focus
I really like Inner Focus. It is useful in many situations. For soloing, it can help get off that last Mind Blast or Psychic Scream to finish off a mob when you are completely out of mana. It really shines in group situations though, as a last ditch heal to save your party. I recommend saving it for Prayer of Healing, which costs lots of mana and is not very efficient. The 25% critical bonus also mean