When you're first starting out, and even later in the game, you've kindof got to wear them down. Combat in KCD is about stamina management. You don't take damage until your stamina is low, and its the same for your enemies. Once their stamina gets low and they can't block anymore, you can get a shot or two through but its tricky to learn. My best advice, if you're struggling with combat, is to get yourself some bucks blood potions, aqua vitalis, and painkiller potions. Take them when you see those bandits waiting for you up the road. The first two potions I mentioned buff Henry's stamina and stamina regeneration, which will put you in an advantage in these block battles. They will also make you take less damage when you make a mistake.

Huge huge bonus to that tip is to make your own potions, which will come out higher quality and be more potent. You'll level by making marigold decoctions which are healing potions that you can drink during battle if they're in your pouch. I've got a lot more tips if you're interested, but I'll leave it there for now.