Observation | Anticipation | Reaction
1: So what's observation, you may ask. Well, it's basically experience. Knowing which styles have loopholes to exploit. Of course, having said that, it applies not just to countering, but to your progress in GA as a whole (which I'm trying to facilitate by training you in this "institution", or what I like to call it). You'll blow by this bit real quick, it's more or less redundant unless you're a low-ranker with very little experience (no offence, really).
2: Anticipation. A meddlesome and tough section of mastering countering. I would've asked you to press XC and C as fast as you can in succession until you're completely used to the configuration prior to this. The sad fact is, anticipation cannot be fully taught. You've to discover the trick to it by yourself, with the method and style varying between different players. Once you know when is the best and sweetest moment to counter for all styles, or even gears, you're done with this.
3: Finally, whatever you've mastered before will come into use as one in this aspect. Reaction. When your senses and your experience merge as one unstoppable entity to catch your opponent by utter surprise and draw exclamations from those in full view of your brilliance. In this section, I'll be fighting against you, often deliberately doing full combos instead of sidestepping to give you chances to show that you've mastered what you've learnt full well. After completion of this entire course on countering, you can set off to put your skills to good use. You'll shed anticipation after a while and by then, you'll be just about as good as me. Countering will be an instinct and will evolve from a defensive precaution into a pressing assault, an offence. That's the beauty and elegance of countering and it's all in your hands.