When increasing your stats, keep in mind that they have the following effects.

Strength
Important melee damage and key to the knight, barbarian, monk and paladin classes.

Dexterity
Improves your dodging, archery, and used for light melee weapons such as the dagger for the ninja and rogue classes.

Intelligence
Boosts magic and magical items.

Skill
Improve critical chances.

Endurance
Calculates your health and ability to wear heavy armor.

Charisma
Reduces costs for goods and training.