Strengths & Weaknesses
Warriors are the most capable damage-dealing class for PvP, simply because of the way they do damage. Rage is the cornerstone of this – the more they are getting hit/hitting things, the more rage and hence the more damage they can generate.
Warriors really only truly shine when accompanied by a healer. They can easily take on a player solo, but the lack of heals or crowd control makes them much less effective without at least one healer backing them up.

The biggest weakness and the biggest strength that warriors have is their dependence on gear. A well geared warrior is truly something to fear, more so than any other class. An undergeared warrior, particularly one without a high max damage weapon, is generally something that can be shrugged off. Warriors scale with gear better than any other class, but it is never easy to get that gear.
Warriors are also quite susceptible to kiting. Two abilities make up for that: Charge and Intercept. Charge is easily counterable, in that it can only be cast while out of combat. If you can put the warrior in combat, using a pet or a long-range spell, for example, then this can severely hamper the warrior’s opening possibilities. They essentially need to hamstring you to have any chance of success, and if you can prevent this from happening, and you have some way of keeping them out of melee range, then you will be at a significant advantage when facing a warrior.
The majority of PvP warrior will spec Arms/Fury with the most important talent being Mortal Strike. Not only is this an excellent source of damage, as it is an instant cast spell with a low cooldown (6 seconds) that is not an “on next attack” skill. The damage at max level is calculated by adding the attack power bonus with the damage of your weapon +160. This can result in some huge crits.
An added bonus of Mortal Strike is the healing coefficient, which reduces healing on affected targets by 50% for 10 seconds. This can really affect healers when facing them 1v1, or when you are chasing a flag carrier, to halve the effectiveness of any heals hey receive.
Occasionally warriors will be Fury specced, but it is far less common and is even more gear dependent. However such warriors are generally particularly well geared, and should be feared.

General Strategies
There are essentially two different fights for a warrior – against melee classes and spell casters. Against melee classes, disarm is very effective, and you generally don’t have to worry about staying in range, as they need to be close to you to deal any damage, just as much as you need to be.
Against spell casters, your main weakness will come from their ability to kite you, and the fact that you need to be at close range to do any damage. Intercept is your friend here, and against priests/warlocks, Berserker Stance/Berserker Rage is essential. You need to be able to remove fear against these classes, and if you are an undead warrior, you have an immediate advantage in that area through Will of the Forsaken.
You need to have a mod or macro that can switch out your weapons quickly. This is especially true for spell casters/healers, where you will need to shield bash to interrupt their spells. Of course you need to know how to effectively switch between stances.
You need to be able to stay out of combat for Charge, so don’t go running into any AoE attacks like Flamestrike, that will prevent you from quickly entering the battle. Obviously, if you are solo, bandages are essential – you will take damage, and sitting to eat isn’t fun, and is also very slow. Make sure you have a good supply of bandages, and use them liberally.
Macros
Berserker Stance + Berserker Rage
This requires multiple presses, but doing so will switch to Berserker Stance and then cast Berserker Rage, to remove fear effects.
/script texture,name,isActive,isCastable = GetShapeshiftFormInfo(3); if isActive then CastSpellByName("Berserker Rage()"); else CastSpellByName("Berserker Stance()"); end;
Battle Shout or Heroic Strike
Not the best for PvP, but this helps if you forget to cast Battle Shout. This will cast Battle Shout if it is not active, or will use Heroic Strike if it is. You can switch out Heroic Strike with another spell if needs be, like Mortal Strike or Bloodthirst.

/script local z=0 for i=1,27 do t=UnitBuff("player",i) if (t and string.find(t,"BattleShout")) then z=1 break end end if z==1 then CastSpellByName("Heroic Strike()") else CastSpellByName("Battle Shout()") end
Arena
Warriors in arenas are most effective if specced Mortal Strike. 33/28 builds, with points in Second Wind are very common. The damage potential of Death Wish and Mortal Strike is huge, and the immunity to Fear is also very valuable.
It is your job to charge into the opponent and soak up damage while causing as much as you can. High armor, resilience and stamina help a lot if you are being targeted – but don’t sacrifice your damage-dealing potential, because it can be huge.
Pop trinkets when you can. This will help with burst. You Insignia should be saved to remove snares, as this is the major problem faced by warriors. With Second Wind, you should have more rage than you can use, so Heroic Strike should be used often.
If you are the sole warrior in your group, use Commanding Shout in the preparation stage, and then once you are out of range of your team, switch your own buff by using Battle Shout. This will help everyone else survive longer, and allow you to do much more damage.
Don’t forget to use all you cooldowns – Intimidating Shout, Death Wish, and any trinkets and racial abilities should be used every fight, because they will be reset at the start of the next battle. If they have a rogue, start in Berserker Stance, as you can remove Sap with Berserker Rage.