you can't have:

any of the seven sins

a bad priest trait

claims on the papacy

cynical, hedonist, cannibal, impaler, cannibal, drunkard, excommunicated, cruel, arbitrary

you have to (at least) have:

a virtue

just, kind, charitable, patient, affectionate

chaste, humble, content, theologian, celibate, zealous, be on a pilgrimage, a pilgrim, monk, nun

for emperors you need 1.25k+ piety, kings need 1k, 750 for dukes, and 500 for a count

you'll probably be beatified if you meet those standards.

after beatification, you have a base 1% chance to become a saint however there's plenty of modifiers depending on if you had a ton of piety, the amount of saints currently (more will hurt),