Fully ascend an attack champ to get the final ascension crit damage stats (63% for legendary, 60% for epic, 57% for rares) 
 
With masteries: get crit rate on tier 1, crit damage on tier 2, crit damage on tier 6 (offense mastery tree) 

Get crit damage amulet, at least 5*

After that you'd only need to find 55% crit rate and 24%(leg)/27%(epic)/30%(rare),

Therefore the easy way would be to wear 5* crit rate gloves, find the remaining 5% crit rate and the crit damage on substats and/or set bonus from crit rate/crit damage set.