During combat, you can click the right stick to lock on to the enemy in front of you, and flick the stick left and right to switch between enemies if there's more than one. Where possible, try to combine this lock with sidesteps or rolls to get behind your foe as they attack, then perform a standard attack from directly behind to execute a backstab to deal much greater damage. All enemies have standard attack patterns, so be patient and study their moves so you can judge when best to strike.
When you perform a roll, you have a brief period of invulnerability during the animation, so practice this technique during combat and work on your timing, as this is particularly useful during boss fights. Bear in mind that if your Weight Ratio (displayed in the top right of the Equipment screen) is below 70% then you'll roll faster and further, and that any weapons equipped in the 1-3 slots of either hand count towards this weight - but items carried in your inventory do not. Equip only the weapons you currently need to get this ratio down and you'll be much more manoeuvrable.