Combat is leveled by fighting monsters.

Chemistry is leveled by crafting potions.

Destruction is leveled by destroying items.

Explosives is leveled by crafting bombs.

Farming is leveled by planting and picking trees and vegetables.

Fletching is leveled by crafting bows and arrows.

Mechanics is leveled by crafting magic and ranging items.

Metalwork is leveled by crafting melee armor and weapons.

Mining is leveled by gathering ores.

Stealing is leveled by stealing from stalls and creatures.

Survival is leveled by fishing, cooking, and firemaking.

Trading is leveled by buying and selling items.