Creating this on the fly so I won't procascinate further on it. Post any useful hints and tips you have here.
Parrying is an important part of high-level Dark Souls play. For more basic information on parries, see the page (when I or another contributor gets around to creating it). The most important thing to know about parrying in PvP is that it does not work the same way it does in PvE. In PvE, parries are timed visually: the instant the enemy weapon should connect to the player is the instant the player should parry. In PvP, parrying is usually done a split second BEFORE the hit connects. Attempting PvE parries in PvP will result in failure.
In general, there are three different types of parrying that are used in PvP.
1). Block and Parry
The Block and Parry involves blocking the first hit of a big, slow weapon (such as claymores or Black Knight Greataxes) and then following the block with a parry. The first block should give the defending player a precise window to time the parry. Block and Parry has great success against weaker players, but has limited success against more experienced pvpers, or people who use fast weapons. To not get B&P'ed simply do not spam attacks.
2). Parry Spam
The act of spamming the parry button. Parry spamming works particularly well against small, fast weapons that deal light damage. The player trades precision for a powerful tool against attack spammers. What are the counters to this?
Parry Spam Punisher
This one's one that I developed myself! Well, sort of. I made it up on my own but I'm sure other people have gotten the hang of it. This works particularly well with fast weapons, although in theory it's possible to do it with slow weapons.
Parry spamming is the act of mashing the parry button when the opponent starts spamming attacks, in the hopes of getting a lucky parry. Parry spam punishing is the act of causing the opponent to parry spam, and then punishing him/her with a backstab. This is possible because the character model does not turn with the player if he/she spams parries, leaving his or her back wide open.
A successful parry spam punish will deal a huge amount of damage, partially due to the weapon spam beforehand (hopefully with bleed build-up) and the backstab afterwards for no reciprocal damage. I know it sounds risky, but I've attempted it perhaps 5 or 6 times and it's never failed for me. I believe that parry spam punishing works so well because skilled opponents see people who spam attacks as newbies that couldn't possibly know about things like punishing backstabs.
3). Prediction Parry
The most advanced type of parrying, and probably the only one that is applicable at high levels of play. Prediction parries rely on anticipating opponent's moves-do they often do a rolling attack? Do they swing twice, and then back off? Do they like to follow a sorcery, pyromancy, or miracle with a lunging attack?-and then punish their predictability with a parry. This one requires by far the most skill, patience, and practice to master.
Every PvPer's bane and most useful tool. Chain backstabbing involves backstabbing, positioning yourself so that you are behind the opponent, and then backstabbing again. This obviously leads to massive damage.
Countering Chain Backstabbing
Simply don't move after you get backstabbed. If you attempt to roll away, your back's hitbox is still in front of the guy. If you don't move, then you will automatically pivot and face the opponent as you get up. Other players have suggested attempting to parry attacks as you get up, and it could work, but don't expect it to work every time: the parries would only work if the opponents precisely timed attacks with the right sort of weapon in the first place.