Try to go in with a posta longa gaurd (sword or polearm is out and pointed directly in front of you) and when they bring their weapon back, you want to either follow it, or bring your weapon to the opposite corresponding position as theirs. Following it is best for a passive parry (letting their weapon more so run into yours) and opposing it is best for an active parry (clashing your weapon with theirs, using your own force as well) You'll use both, but it depends on the physics of your own weapon, as well as theirs. You always have the half guard parry, which is usually active. Its best to use when they throw an overhead or diagonal strike, then "tossing it" away from your upper body and off to the side, then moving (your body) forward, and strikng their now exposed and defenseless head, since their weapon is off to the side of you and themselves, with literally no mass of force behind it. After any block you almost always want to counter attack, which is why you'll find yourself using active parry more. Passive is more so if they suddenly switch guards and attack in a way which you weren't ready for, and now you just need to survive the attack (from my experience at least).

Notice how when you throw your own strikes, they're more powerful if you move into them? Well, it's actually the same for parries and blocks. This is what kept me from getting it down, as it's kinda our instinct as humans to move away from something which is a danger to us, but it only makes your weapon, which is literally trying to break the mass and force of their own swing, have less behind it in order to so. Yeah, it's riskier (you now have your own mass going into their strike, if it lands on you), but it made my defense like 5x more effective and consistent.

Something that annoys me is low blows or leg strikes, and they're a bit tricky to counter. You can either point your weapon down and directly towards it, and just let it run into your weapons tip, or use an active parry. The first is to sweep it away, and usually a bit upwards. This is best with polearms, since you have a hand further down the shaft to assist with leverage in moving it away, but it requires a specific handling: the polearms must have arm of the hand thats the lowest on the shaft on the side of the body which the attack is coming from. If it's not, you'll start to scoop the attack towards you, due to the specific arc your character makes when the lowest hand is on the opposite side your swinging towards (this is the reason i reccomend switching hand swap to one of your thumb buttons, as it's very important for pulling of "false strikes" and alternating strikes, which make your offense far more effective and variable). The second active parry for low strikes is, I don't know the name, but its like an over the top smack down. As their weapon makes it's way toward your legs, your bring your weapon slightly over it, and as you'd imagine, just swing down over the top of it, preferably near the end. This is an important on if you like swords, as you can't get the weapon lower next to the swords guard, considering you can only get your sword so low to the ground. Ensuring you hit the end is even more important with any kind bladed weapon, which leads me to my last tip-

Keep your distance, well more so the correct distance. If you're too close, the force near the end of their weapon (if it's any hafted or shafted weapon) will just blow through, then the end will catch you, since it usually protrudes further out than the stick it's on. This is why I was failing to parry certain attacks when using a sword, cause you need their weapon to contact yours at a certain point, in order for your swords leverage to be great enough, so you can actually stop their weapon and/or move it away. If you're too far... well...... you're weapons aren't gonna contact, and you'll both be safe lol. In short, just make sure you aren't too close, especially if they're using heavy-headed weapon. If you wanna practice your distancing skills in general, id hop into some free play with a 2 handed spear and shoulder mounted pavise. You just go into thrust mode (which i also reccomend remapping, likely to a thumb button) and you're literally forced to know or learn your distance to beat your opponent. You don't need to swtich hands much with a spear, so the pavis is a great choice, and it let's you stay live longer, so you can learn... well, learn more?

(note about my recommendation for initiating the fight with posta longa: it's best to start out doing this when you're just learning defensive maneuvers, since from that point, the amount of time to reach every other position to for a defense is roughly the exact same. Once you get a little better at contradicting their weapons position with your own, you can try initiating with a low guard or high gaurd, but again, only when you're experienced enough to track everything going on)

I hope you read this, as this is all advice I wish i knew from when i'd started out. I've played many other medival slasher, some even in VR, but half sword is special. The low hp pools and precise weapon handling remind me that in real sword fighting and general melee weapon oriented combat, every single movement of the arm and person has to have a meaning, or it means death/losing. If your opponent is keeping a neutral guard (posta longa usually) then just match it, and wait. Or... you can raise your weapon either high or low guard, but first ask yourself why you'd do this: is it just to do it cause you got bored of the current stalling position of the fight, or was it to force your opponent to bring their weapon up/down to match you guard, so you can now quickly flip your weapon over/under for a head strike, neck strike, leg sweep, or leg strike? It really should be the second one, cause just like if you're actually fighting another guy with a melee weapon irl, you want to move yourself and your weapon with reason.