If an attack is blocked, the attacker takes increased time to recover. That goes for you and the AI, so wait a little before striking, don't just swing around with your weapon.
Here's the main techniques:
Either move in towards the enemy (don't get too close), then step back when he's about to strike, so you can avoid the hit, then move in again and start slamming him (if he doesn't have a shield he usually won't be able to recover from your repeating blows, if he does he probably will, where you start all of this all over again).
OR
Wait for him to strike first, then block his attack, either with a shield or with your weapon (if he cancels the attack, wait till he makes another, because by the time you notice he'll probably have time to make another one). Block, then strike. It takes a lot more time for him to recover in that scenario, so you can start slamming safely.
Use auto block only until you've gotten used to moving properly. Then switch to manual.