Understanding the PvP Prestige systemThe Prestige system is closely tied with the new Honor Level system, in which you level up your Honor Level each time you earn Honor from any source. There are currently 50 Honor Levels, and these levels give you access to new abilities which are mainly useful for PvP. Once you reach level 50 you can choose to Prestige, starting at Honor Level 1 again, and can restart the grind. At launch you would loose all your Honor Level abilities by Prestiging, but this has been changes, so there is really not anything to loose by using Prestige.
There are a total of 4 Prestige levels, and each new Prestige level offers new rewards. In the coming seasons the Prestige level cap will be increased, with new rewards on the horizon for those who wants to climb even higher.
Prestige rewardsPrestige Level 0, Honor level 50:
The reward is a unique Battle Pet. You get the Alliance Enthusiast / Horde Enthusiast, obviously based on the faction you play as.
Prestige level 1, Honor Level 50:
This rank unlocks a set of unique Artifact Weapon Appearance.
Prestige level 2, Honor Level 50:
This rank unlocks an item called Honorable Pennant. This is a pennant that represents your faction, which you carry on your back.
Prestige level 3, Honor Level 50:
This rank unlocks a unique mount, called the Prestigious Bronze Courser. Both factions get the same mount.
Prestige level 4, Honor Level 50:
At this final rank you get a unique title, called Name the Prestigious. Obviously the "name" part will be your character name.
These rewards are the ones currently tied to the Prestige system, but a lot of other rewards such as different mounts and titles have been datamined. They might simply be rewarded for future seasons, or from higher Prestige Levels in the future.
Gaining Prestige LevelsAs said above, to get Prestige Levels you need to hit Honor Level 50. Once when you are level 50, the option to Prestige will be available from the Honor tab. Most PvP actions in the game awards Honor, such as killing players, playing in battleground, arenas or the special PvP zones such as Ashran.
Arenas seems to be the best and fastest way to currently gain Honor, but if you just want a little more relaxed way to gain Honor, battlegrounds are very good.
The Daily PvP World Quests also offer a nice chunk of honor. The regular "cap the enemy tower" ones give 300 Honor Points per quests, and there are three of them available every day. The Free-For-All World Quests give 500 Honor Points, and there is always one available, and they rotate every 4 hours, so you can essentially get 500 Honor every four hours with this world quest.