Ability Points
Ability Points (abbreviation: AP) allow a player to raise their base stats. When a character levels up, they are given five AP to put into their base stats (Strength, Dexterity, Intelligence, and Luck), their Max HP, or Max MP. A player begins the game with 50 HP, 15 MP, and the other stats are 4 with 9 randomly distributed AP.
Just about all jobs have a certain way of adding AP to stats in order to maximize the overall ability of a character. Having even one point assigned to the wrong stat can severely hamper the progress of any character. Almost always, these point arrangements do not include adding to Max HP or MP. The exception is the HP Fighter or Page, who uses Power Guard to kill high level monsters by bumping into them. Once assigned, ability points cannot be taken off a stat unless transferred to another stat by buying an AP Reset from the Cash Shop.
Strength
Strength or "str" is the most important skill for warriors, as well as a sub-ability for bowmen. Warriors should have as much ap as possible into strength. A bowman should ideally have their level, plus 5, in strength, while crossbowmen only need their own level in strength. A magician's strength should be kept at 4 or 5, preferably 4. A thief's strength should be kept at 4 or 5 also, with the exception of strength bandits. Strength increases your overall melee attack ability. Contrary to popular belief, it does NOT affect overall HP.
Dexterity
Dexterity or "dex" is the most important skill for bowmen, while thieves and warriors need it as a sub-ability. Warriors should have dex at twice their level, so they can wear items and hit monsters. This can change at higher levels. Bowmen need to keep their dex as high as possible, as it determines their damage with bows. Magicians need to keep their dex at 4 or 5, preferably 4. Thieves need twice their level to wear equipment and hit monsters. They also need 25 dex to get the 1st job advancement. Dexterity also increases the accuracy and avoidability of your character, which is needed for every class except mages.
Intelligence
Intelligence or "Int" is the most important skill for mages, while, surprisingly, no other classes use it. Mages need their int as high as possible, for their mage attack and defense depends on it. All three other classes should keep their int at 4 or 5, as it is useless to them. Int also determines your mp every level, as well as magic atk and def.
Luck
Luck, or "Luk" is the most important skill for thieves, as they need it to do damage and for their equips, while mages have it as a sub-skill. A thief's luk should be as high as possible, so they can do damage and wear items.
Mages actually need luk in a strange pattern, being as they are the only class with "split equips". A magician meets the level requirements for overalls and wands at lvl 8-13-18-23-28 etc, while stave's, hats, gloves, and boots are at lvl 10-15-20-15 etc. At every lvl for wands and overalls, your luk needs to be at least two more than your level. For every lvl for stave's, hats, boots, and gloves, it needs to be three more than your level. The easiest way to meet these requirements is to simply just keep you luk at three more than your level. Warrior and bowmen should keep their luk at 4 or 5, preferably 4.
MP and HP
Very few builds involve the allocation of Ability Points into HP or MP. The hp you gain from adding Ability points here depends on your class and Strength. The classes that gain the most HP per Ability Point added in this order, from most to least, fighters, pages, spearmen, bowmen, thieves, mages. The MP you gain per ability point added depends on your Intelligence and class. From most to least per level, by class: mages, bowmen, thieves, pages, spearmen, fighters.