The Black Blade Build uses the Black Blade Incantation to open difficult fights, placing a -10% Max Health debuff on the enemy or Boss for a short time from range. This HP does not come back once this buff expires, so it's only necessary to use this once per fight, but you can use it again if you need a ranged option.

Ideally you want to use Destined Death from Maliketh's Black Blade immediately after this because Destined Death also applies a stacking -10% Max Health debuff. If both of these are applied at the same time, then the enemy or Boss loses 20% of their Max HP that doesn't come back. However, if you wait for one of these debuffs to expire before placing the other you will not get the extra 10% Max Health reduction. So time them close together for best results.

Use Golden Vow to boost your damage and defenses, and Blessing of the Erdtree to keep your HP topped off. You can add other Incantations if you want because you'll have decent Incantation Scaling with the Clawmark Seal since you prioritize Strength and Faith.

Use Jump Attacks on regular enemies, and remember that R1s and R2s with Maliketh's Black Blade have some hyper armor, allowing you to attack through other attacks most of the time.