For World of Warcraft, engaging in PvP for Hunters is the key point. For some players, they may make mistakes, but they utilize techniques that are beyond a simple computer's ability to execute. In this case, World of Warcraft is an example. Just like an NPC controlled Rogue won't try to run behind you to use the backstab ability, but a player controlled Rogue will, making the task of defeating your opponent all the more difficult.
If you're a first time PvPer, it's important to put everything you know about PvE combat out of your mind. Think of it this way, PvP and PvE are like apples and oranges, relatively similar on the outside in terms of shape, but extremely different on the inside. Just standing there and blasting away in PvE just won't work in a PvP situation.
The strategies we will talk about are useful for levels 1-55, and perhaps till 60. We are not necessarily claiming that these strategies will work beyond level 55. The below techniques are utilized by my peers and I to great effect. I'm hoping they'll benefit you as well.
For the most part, Hunters use their pet as a tank when engaging in PvE, but in PvP your pet is used for pure damage, since taunting doesn't work against PCs! With this in mind, I'd advise getting a pet that is high in DPS to use solely in PvP. Cats are usually the best choice for damage, and although cats may die faster than say a bear, the damage output is well worth it. Most of your opponents will not go for your pet instead of you, unless you're in a duel. Personally, I have a bear and a cat, the bear is for tanking in PvE, and the cat is for damage in PvP. The link section below can help you find the pet that's perfect for you.
For Hunters, Aspects are arguably the strongest set of abilities for them to have. In melee, they're always activating AoM, except against Warriors! They have an ability called Overpower, which "Instantly overpowers an enemy, causing weapon damage plus X. They can only be used after the target dodges. Overpower cannot be blocked, dodged, or parried." Even worse, there's a Warrior talent that can cause Overpower to have a 50% critical chance! Against any other melee combatant though, activate AoM! In ranged combat, use AoH.
Both in PvP and PvE, tracking is an invaluable skill. The most valuable tracking skill is Track Humanoid, as it can alert you to an opponent long before they reach you. You might be asking "What about Track Hidden?" For our part, we find Track Hidden to be nearly useless; the range of tracking is so limited that by the time a Rogue shows up on your mini-map he's already within striking range! Besides, Freeze Trap and Flare are much more useful against stealth opponents. We'd recommend keeping Track Humanoid on at all times in a hostile area, unless you feel the need to see where beasts are with Beast Tracking. You might have noticed that we didn't mention Track Undead, which many Alliance players may mistakenly use to track an Undead PC, however, Undead PCs are considered Humanoids, only NPC Undead are tracked using Track Undead!
At length, some Hunters have a habit of "spamming" shots, or using abilities when they aren't needed. Often Hunters make use of Concussive Shot and/or Stings when either it's already in effect, or it's simply not needed. The only ability you should be using constantly is Arcane Shot, as it does damage. Concussive Shot is useful for slowing your opponent, and Stings should only be renewed when they wear off, rather than every time they're available.