I did this at the start of the game during the combat training against Vesimir. I followed the tutorial and then it let me free fight or sheath my sword to finish, I continued fighting.
I equipped the Yrden sign (Hold L1 and highlight it), then I pressed R2 to cast it. This puts a circle on the ground that slows Vesimir down. I then pressed L2 as he started attacking to perform the counter. I did 2 or 3 counters and then recast Yrden again. After 10 counters, the trophy unlocked.
A big advantage to doing it here is there are no extra enemies to worry about and you can keep trying until you get it since this is a training section. Obviously if you have passed this section of the game and want to go for it, then the above tips still apply, just perform them on any human enemy for an easier time