Leveling a warrior for the first half of the game is probably the most annoying class with which to do so. We have few abilities, and do not come into combat 'fully loaded' like mana and energy users. Our class and role defining abilities, some essential to the talent schools, do not come into play until the 20s and late 30s. It is very important that we channel our rage (quite literally!) into the most efficient killing tools to maximize our killing speed.  We have no ability to self heal, so minimizing the damage taken over the course of combat is required to avoid the downtime of food or a bandage.  Downtime also equals a total loss of rage probably, further impacting your killing ability.  So without further ado, let us analyze ways to open, handle, and close our fights with the proper amount of force, speed, and rage management.
 
The Opening - First Phase

Rule #1 of playing a Warrior:
Battle Shout is up unless you have a better attack power buff.  No questions asked here, it's a solid bonus to all damage we do.

Rule #2 of playing a Warrior:
If you want to attack something, Charge it. There are next to no exceptions when soloing and leveling up that you would rather use a more passive opening. The only time I would not charge a target is when I'm slaughtering the fools so fast that it's still on cooldown. If you are protection or fury and want nothing to do with battle stance, there are two things to remember.
 

• A charge and melee blow will give you enough rage for an immediate improved thunderclap as protection.  You can then switch to defensive stance and start your sword and board style with no rage lost assuming you start from zero.
• You can hit any of your shouts mid-charge, and for that matter, any area of effect ability that is centered around you and doesn't require a target.  Berserkers can hit battle shout the moment they charge, and hit berserker stance by the time they reach their target.

  
You can never go wrong with using Rend on a target early in a fight.  Unless you are going to utterly destroy it in two seconds, taking your initial charge rage and landing a Rend is always a good decision for stacking a fair amount of damage over time for a minuscule 10 rage.  Since virtually everything in the game is now vulnerable to bleed damage (Thanks, feral druids!) you should expect to lead off with Rend in every fight.  If the fight is an elite, a double or triple group or has pets involved, you will likely want to throw out a Thunder Clap early as well to lessen the damage done over the course of the fight, and the same goes for Demoralizing Shout.  Both will lower the damage you receive by a very noticeable percentage.
 
The Toe to Toe - Middle Phase

You must pick and choose your moves well for your situation.  Heroic Strike is not your go-to move for every single 15 rage you accumulate.  Once you land your initial debuffs, single targets can be dealt with in different ways depending on your style.  Until you learn instant strikes, Sunder Armor is how you'll spend your rage for the first half of a foe's life as a dual wielder since the negative armor increases your fast white damage drastically.  Arms warriors will be spending their time watching the Overpower icon like a hawk to see when they can get a free 5 rage shot, and landing a sunder or two of their own.  Protection will be looking for Revenge opportunities and sundering in between them.  If you ever find yourself with a half full rage bar, that's when you should be hitting that Heroic Strike button.
 
Fight or Flight - Execution Phase

If the foe is a speedy runner, at about 20-30% you will need to land your slow if you are in risky, highly social territory.  Protection warriors will be bashing with their shields, or landing another rend to run around bleeding to death.  As arms and fury, you have two options - Execute (Level 24+) or Hamstring.  Hamstring is a safe option, and combined with rend can give them a slow death sentence.  Execute is often seen as the best option, but you have to weigh if your current rage is best dumped into the execute or the next enemy.  If you have more than 50 rage, you probably shouldn't execute if you have another target nearby since you can use that rage to lay into the enemy very quickly.  You do not have to go all out to finish an opponent off unless the situation you're about to get in by chasing and wailing away will result in a painful death.
 
Protection Specific - The Angry Mob

This strategy revolves around getting 4 or more melee enemies in front of you and using your superior mitigation abilities in conjunction with counter attacks and more potent, cheaper Thunderclaps to take on groups of enemies.  Thunderclap should be used every time it is up.  Once the enemy is fully engaged in front of you, hit shield block and revenge every time you can. Tab through and use Rend on each one when revenge and Thunderclap are down.  When shield block expires, hit Berserker Rage if you have it to assist in generating rage for your offense.  You can interchange opening with the rage, and using the shield block second if you prefer a more potent opening filled with Cleaves.  You may think that the rage reduction glyph for Thunderclap is required for this, but so long as you have that lovely 2 Rage generated on block, you should have plenty from your melee attacks and shield blocks.  This can be a little dangerous with social humanoids, but you should probably leave them to bleed out when individuals turn and run so you can keep the opponents in front of you for your blocking and mitigation purposes.  It's also important to note that this is a lot more fun than just picking on singles like have you been for 20 levels.
 
A Defensive War - Soloing Elites

It's rare, but on your way to 40 some quests may have you struggling to find a group to take down elites to end a quest line.  You'll need to engage with a one hander and shield in hand, at least initially.  Engage however, and quickly throw up Demoralizing Shout and Rend it.  Shield block once you're exchanging blows, and drop Thunderclap.  When Shield block expires, hit Shield Wall and continue.  Refresh Rend and Thunderclap as Shield Wall expires, and expend any remaining rage on a Heroic Strike if you're going to be switching it up for the next part.  From here, switch to your preferred stance and fight it out.  If you are switching to battle stance, do not be afraid to hit retaliation, especially if there are multiple enemies.  If they have allies that aren't going to grab more, use Intimidating shout at this point to make it a 1v1 while you're in an offensive mode.  Finish strong, and use Execute the moment it's up, Bloodrage, and do it again to more than likely end the fight.  A lot of people don't use multiple high cooldown disciplines in one fight - don't make this mistake!
 
Our Ideal Foes, and Foes to Avoid

We absolutely love rogue type enemies.  We have high physical mitigation, gain rage when hit and much more so when Berserker Rage is active. Rogue types tend to dodge more, and that is a blessing rather than a penalty to us. Protection types have a field day with block rage generation. The only special ability some have rarely that annoys us is Disarm. Avoid casters like the plague.  Frostbolt casters, more so.  Frost nova casters, even more so!   They have less hp and armor, but tend to always be runners, and runners that can be a complete pain to catch and love to tell their friends to do the exact same thing to you if you don't finish them in time.  We have a few methods to interrupt casting, but instant cast immobilizations will cripple us until we get very far down a talent school.
 
Quests
 
Path of Defense

Your first main quest is to get a solid one hander and defensive stance.  For instance, for Kalimdor Horde, you can find the start of this over the bridge to Durotar from Uzzek.  Completion of this will get you access to Sunder Armor, and Defensive stance.  Getting accustomed to this stance is essential to being a good warrior, so do it quickly so you can do the second part!  The second part has you going to another NPC to get your one handed weapon made. To continue from the previous leg, you'll find Mr. Firegaze atop the mountains covered in brambles to the southwest, surrounded in bristlebacks.  Be cautious, for they'll be higher level than you at this point.  A hop, skip and a jump north to the broken caravan for the quest reward will get you a good weapon to use for the time being if you prefer the slow and steady one hander and shield approach.
 
Brutal Armor

This quest, obtainable at level 20, will provide you with a solid set of armor parts for the mid 20s, and very early access to a helmet.  For the Horde, you'll return to Thun'grim Firegaze in the Barrens and ask for a set of materials which are all but impossible to obtain yourself at that level.  Assistance from your friends for the trip to Razorfen Kraul, and the auction house if you're not a miner, will net you the Brutal Hauberk and access to the other 3 parts.  One will send you to Durotar, one will send you to Undercity, and one will send you to Thunder Bluff to fill out your armor set with high quality items.
 
The Islander

At level 30 you'll be sent to an island east of Ratchet for a survival bout to obtain Berserker Stance.  Talking to Klannoc Macleod will start the contest.  Multiple lesser opponents will engage you one at a time, and using Demoralizing Shout will send them running in fear for free shots.  They should pose no trouble for you.  Once you get an announcement of Big Will jumping in, you have some time to bandage and prepare.  Charge him, and fight him as if he was an elite using a strategy similar to the above if you're having trouble.  Achieving victory here will give you the all-out offensive Berserker Stance, and the follow-up below.