Leveling as a Prot Warrior is actually pretty fun......once you get past a certain level. I think 40 is when it starts getting better as that is when you pick up shield slam. Punching people in the face with a shield is the shit.
Before that, leveling as Prot is just as shitty as leveling as Fury or Arms. You have rage problems galore and not enough damage abilities. Heroic strike spamming is FTL.
Shield slam is really good, but where is really gets interesting is when you can pick up sword and board for juicy Shield Slam Procs.
I am not going to lay out an entire guide today as I am way too busy being delicious. I am just going to put out some rotations for prot warriors once they start to get into the magic levels (past 40).
Soloing: Questing is good. If you are just hitting Outland or Northrend, you will be picking up tons of upgrades. Your rotation is pretty much going to stay the same once you hit Outland. You are going to charge in (WARRRRBRIIINNGAAAAAAA) and shield slam them in the face. Hit revenge whenever it procs as it is very good damage as well as fairly low rage. I still run with the glyph of revenge for the free Heroic Strike after the revenge.
You will also want to spam devastate as much as you can. Not only does it hit pretty damn hard (critting for 1400+ for me as a 63 Warrior on my Horde toon), but it has a chance to proc Shield Slam if you are talented into Sword and Board.....and you better be.
If you are AOE grinding, depending on the number of mobs, you will work in Shockwave and Thunderclap in there. I would also use the glyph of cleave and make sure to cleave in all high rage situations.
Groups: Groups are easy. There is an AOE rotation and a single target rotation.
The AOE rotation for me is charge (once again WARRRBRINGAAAAAA) and Thunderclap. Back up a few steps and shockwave them. Remember that you will not be generating much rage for a few seconds as the mobs are stunned. When they are unstunned pop your shield block (nice AOE threat with damage shield). If you are drowning in rage feel free to spam cleave (once again, I glyph for cleave). While hitting Thunderclap every cooldown and spamming cleave, I like to hit shield slam and Devastate with every other available global cooldown. Remember not to use shockwave again if the mobs are going to be dying quickly. You want it to be available for the next group.
The single target rotation is simple. Charge in (or shoot if you dont like charging bosses) and shield slam them in the face. I then like to devastate spam for lots of Sword and Board procs and Heroic Strike when I am over 50 rage. If you are getting low on rage and revenge lights up, use it. Especially if you are glyphed for it.
Devastate was buffed to the point where some people are going to stop using Revenge entirely. Not I. I have a feeling that Revenge will be getting buffed before too long as well (I believe Ghost Crawler said as much). So, may as well keep it in your rotation for now (especially if you are talented and glyphed for it).
That concludes today's prot Warrior leveling guide. Get out there and shield slam some faces.