Think about it, observe their behaviours more closely, can you spot anything that's off about them? Is there something they get particularly worked up over? Have you seen them bully other people? Can you spot any techniques they use to intimidate people?
The first step to taking down an enemy is learning what you're dealing with, this is the stage you're at right now. Meanwhile I suggest you grit your teeth and bear anything they send your way, if they beat you up, get right back up again and smile, even if you bleed, keep smiling. Pain only lasts for a bit, it goes away, they have no power over you if you don't fear pain. And don't worry, it won't hurt as much when it happens enough, you'll get used to it.
I suggest you look at your advantages and disadvantages too, are you a particularly good tinkerer? etc