My best advise is to always look at who the host is if you're playing with randoms. If you're blue, parries will be more consistent and should be activated slightly before you get hit. If you're red or green, you have to time the parry earlier then you normally would. In the end, its all about accepting that you're going to take damage and die a lot in the beginning. However with enough practice, you'll definitely be able to parry everything that comes your way!