[Update #2]: Blackwing Lair, level 50 class quests, and a whole bunch of other content are coming to World of Warcraft: Classic this February 12th!
[Update]: Warsong Gulch and Alterac Valley battlegrounds have now made their way to World of Warcraft: Classic!
If you're on a PvP server, make sure to stock up on a variety of potions as Phase 2 has now arrived to World of Warcraft: Classic! In other words, PvP ranks and rewards have now finally become available, as have the two original world bosses: Lord Kazzak and Azuregos.
In order to advance through the PvP ranks you'll need to kill players that are within ten levels of you, as well as take down the various faction leaders for a sizable boost to your honor. However, do make sure not to attack civilian NPCs or players that are far below your level as that will grant you dishonorable kills, each of which will provide a fairly significant reduction to your honor.
Unfortunately, the battlegrounds are still not available, and so the only way to gain significant amounts of honor is by attacking enemy players out in the world. As such, I will once again recommend you stock up on potions and defensive items and as you'll undoubtedly run into ganking parties while out in the world, especially in some of the late-game leveling zones since those tend to be the easiest ones to target for dedicated PvP players. The Plaguelands are particularly notorious for this, as they have been a ganking hotspot even in the original World of Warcraft.
On the other hand, if you're not a fan of 'pointlessly' fighting against your fellow players, the two new world bosses should provide an interesting challenge and a real reason to bear down upon your opponents. Since the bosses are freely roaming the world, you'll need to compete with both your fellow players and the enemy faction in order to take them down, and much like in the original World of Warcraft, that's always going to be a glorious mess!
You can learn a little bit more about the two world bosses, as well as PvP ranks themselves, over at the official website.