Damage Calculations

The Damage Calculation 
Damage Modifier * ( Pierce * ( 1 + %Pierce ) + ( Attack / 6 ) - (( Defence + Block Defence - ( Ignore * ( 1 + %Ignore ) - Defence Debuffs ) / 2 )) * (( 100 + Critical Power ) * Critical Rate ) + ( 100 * 1 - Critical Rate )) + Fixed Damage / 6

Simplified (No Ignore, No Pierce and with 100% Critical Rate):

Damage Modifier * ((Attack- Defence) / 2) * Critical Modifier + Fixed Damage

Damage Modifier are modifiers affecting the damage such as skill damage modifiers.

Attack is primarily all the additives multiplied by Base Attack

Base Attack is basically (Weapon Damage + Soul Stone + Base Stats).

Critical Modifier are the modifiers affecting the Critical Power and Base Critical (100).

Recommendation for building Damage

Huge damage is usually obtained by combining at least 3 of the 4 below:

1. High Damage Modifier
2. High Critical Modifier
3. High Base Attack
4. High Frequency of Attack (whether 0s skill cast time or high attack speed)