Cleric

Clerics are the healers of Aion. This class is very important because much like buffs, heals are needed for the higher level, end-game content. They are also extremely helpful during PvP combat.

Playing a Cleric is one of the easier classes, as long as you are very attentive to what is going on around you. Whereas the buffer just needs to ensure they are getting everyone buffed on time, healers have a much more proactive approach. Your goal will be to watch everyone's health and ensure everyone is alive and kicking. Going away from your group for even a small amount of time, without telling them, can cause everyone to die, including yourself.

Some players do not like being a Cleric because, much like with tanks, you are expected to be paying attention the entire time you are hunting (or PvP'ing). To others, however, this is a good thing because it keeps your job ever-changing, and allows you to keep your concentration on something, rather than sitting there assisting other players all day. This is really your choice, though.

Strategy

The Cleric strategy is a fairly easy one, but it does take time to get used to it. The basic principles you  need to learn are:
.How long your spells take to cast
.How much health your allies have
.How much you are able to heal for
.How many heals you can throw out before resting
.Who takes the most damage in your group(s)

Being a healer is significantly easier if you are playing with the same group of other players most of the time. This allows you to better adjust since you learn exactly how to cope with your group. But what happens when you have randoms?

The player you choose to heal at the time is not always the one with the lowest health. Let us say that you have four players in your group: You, a tank, and two damage dealers. Your tank is at 50% health and your damage dealers are at 70% and 75% and both are being attacked by enemies. In this case you would want to heal the damage dealers because they will take more damage than the tank. Being that tanks are built to "tank" damage, their health, although it seems like less, will last longer than the other classes. The same goes for other healers or mages.

Along with this, you need to learn how to manage your healing as efficiently as possible. There are many players who have no issues with getting to low health, as long as they trust you as a healer. This allows you to rest more in between each heal, thereby giving much less downtime than you would experience otherwise. If you can heal for 50% of someone's health, for example, do not use it until they are down to half health. Using a heal earlier will just waste your mana, causing more downtime than you would normally face.