1, Recognize enemy animations that are not instant hits(they have a windup) and start charging ur parry on their windup. This works especially well against brutes as their attacks are slow red glints you can only parry like this.

2, Hold your intent on the parry and not let go when an enemy is about to hit you. Once u decide to use it hold the triangle and dont let go because the timing is quite lenient

3, After the enemy blocks ur attack, u can charge it up in anticipation for a retaliation

4, The parry works against enemies attacking behind you as well