Increased Critical Hit Damage

Increased Damage can be achieved by buying, trading for, crafting or finding a high DPS (Damage Per Second) weapon for yourself.  Other types of gear and enchantments can also increase your damage.

Equipping certain gear and choosing particular Skills can Increase Critical Hit Damage.

Also See:
Critical Hit Bonuses
Increase Critical Hit Chance

The Following Is A List Of Each Class' Skills That Will Increase Critical Hit Damage:

Barbarian Skills That Increase Critical Hit Damage

Ruthless (Passive Skill)

Demon Hunter Skills That Increase Critical Hit Damage

Strafe (Stinging Steel)
Archery (Passive Skill)