Here is how I do it and by it I mean work on a counter to a move:
I play the role of the attacker and my partner plays the role of the defender and I attack and I mean ATTACK and when he tries to counter by the move I THINK may work, I COUNTER THAT MOVE and if I can, well, that means it may not be as good a counter as I thought.
See, first rule of thumb is WILL THIS COUNTER WORK ON ME IF I WAS DOING THAT ATTACK?