General Information

There are lots of little bits of information that are useful, but don't fit in any particular section and are too short to be worth making their own section. Information like that can be found here.

See also Abbreviations and Terms.

Combat Related

Note that there are three areas of combat: land, air, and water. Attacking something in one area from another area causes a reduction in both the damage dealt and the damage received. For maximum damage, make sure you attack land mobs while on the ground, water mobs while swimming, and air mobs while flying.

There are some common names for how some skills affect their targets, here is what those names mean (the first name for descriptions that have multiple names is the actual name of the status effect):
Frozen, Paralyze, Bind, and Immobilize = Unable to move, but can attack (assuming it's in range).
Total Intervention, Silence, Seal, and Chaotic = Unable to attack, but can move.
Sleep = Unable to move or attack until hit (pre-existing DOT effects will continue doing damage and will not end sleep).
Stun = Unable to move or attack.
Freeze = May either mean the same as Frozen or the same as Stun, depending on source. The Occult Ice genie skill causes a stun-like result called "Freeze", but anti-stun buffs won't prevent it. Whereas some skill descriptions say that they freeze the target, but they actually do a Frozen effect.
Note: The cleric's "Silent Seal" skill does not cause the Total Intervention effect, as you might expect from the name, but it actually causes the Frozen effect instead.
For more on status effects, see the Status Icon Reference Guide.