This isn't a specific gearing guide - you'll have to find out what items you need based on the stats outlined. Likewise, there is plenty of spec information available out there, so I'm not going to repost it.
I originally wrote this on my guild's private forums, but I figured I would share with you guys too.
How to raid as an arms warrior
Arms is not going to give you the best personal DPS in the world. Other classes, and other specs, will take that role. However, arms DPS is not bad - at all. It is very competitive with Fury, when played properly, and it also offers some advantages, such as Blood Frenzy and Trauma.
What do I need as arms?
Hit: 264, or 8%. This will hit cap you. If you are below this, make it your first priority. This is WITHOUT the draenei racial hit buff. If you know you are going to have it the majority of the time, then you need 7% hit.
Crit: 35% In battle stance
This is a very good starting point. Raid buffed, you're going to be at around 45% crit. Your goal is eventually 50%, as this will mean EVERY overpower is a crit, making it easy to keep up deep wounds and trauma.
Attack Power: There isn't any set number. AP is multiplicative with hit/crit/etc, meaning that it gets better as those get better, and visa versa. Do not go full crit to sacrifice AP, and don't go full AP at the expense of crit.
Expertise: The cap is 6.5%. If you were to attack from the front, this is a more economical stat than hit, as you get 1% dodge reduction and 1% parry reduction. If you attack from the back, this stat is as economical as hit. In most fights, you should be attacking from the back - but there are some where this is not always possible. Once you hit cap, it no longer matters, as you will not be parried or dodged.
Haste: Haste is a very neutral stat. It takes large amounts of it to reduce your swing timer, but can have significant effects on your play style when it does. Not many of our skills are really better with higher haste. Don't stat for it, don't ignore it. It's not bad, but it's not really good either.
Armor Pen: ArP is a very confusing, and for an arms warrior, almost useless, stat. Percentage based armor reduction, such as mace spec, applies after all static reductions, such as sunder or expose armor - meaning that you're taking 15% off of 6k armor instead of 16k. Static reductions are a bit better, as the more armor removed from the equation, the more valuable the stat is, but it is largely a stat not worth the itemization points. This could change in the future, depending on design decisions, and is hinted at due to the large amounts of it on warrior tier gear, but at current, it is not a good stat to gear for.
Raiding
Alright, you've got your gear setup, and now you want to kill stuff. Fair enough.
Arms does not have a DPS rotation. Instead, we have what largely amounts to a priority list, depending on how much rage we have, and what procs we have available. However, one thing never changes:
Keep rend up at all times.
Rend ignores armor. It applies one of our raid buffs. Many of our talents depend on, or improve, bleed effects. So keep it up. It is your first priority.
But don't refresh it before it falls off. Rend ticks 3 seconds after you apply it, so you lose at least one tick in damage if you apply it early. The one exception is when you are going to be out of boss range - Anub'rekhan before he swarms, Heigan when you're about to dance, etc. Then refreshing it to keep it up while you will be out of melee range is needed.
Get your glyph of rend. Now. Having it will free up your GCD multiple times per fight, letting you throw in that slam, MS, execute, overpower, whatever, for that GCD instead of having to rend. This can mean a huge DPS increase.
Sub 20%, in execute range? STILL KEEP REND UP. Period.
There is no set rotation.
Besides rend, it becomes much less rigid than you would see with, say, Fury, where an improper rotation will cause collisions between abilities and wasted GCDs.
1) Rend. See above.
2) Sudden Death execute / Overpower. If both are lit up, use execute FIRST. SD Execute will leave you with enough rage to overpower right after
3) MS/Slam. If you have enough rage to use MS, use it. It doesn't interrupt your swing timer, like Slam does. If MS is on cooldown, or you have a free GCD without enough rage to MS, then slam. It's your lowest priority on the whackamole skill list.
If your swing timer gets down to about 2.5 for melee hits, slam can actually be a DPS reduction, as it pauses your swing timer. In this case, if MS is on cooldown and you do not need more rage from the next melee hit, use heroic strike. This will be very rare, as you should not be gearing for haste, meaning only in certain situations for short periods of time will you likely have enough haste to be in the 2.5/2.6 swing range.
Bladestorm is a powerful tool, but it's hard to decide when best to use it. On fights with adds, it can be extremely useful for damaging them and the boss. On Sartharion, I pop a trinket, use sweeping strikes, and hit bladestorm while in range of both the boss and the adds, allowing me to hit all of them. In single target fights, I try to use it every cooldown to build rage and proc sudden death. I particularly like it in AoE situations where it's also likely it will get me a killing blow, allowing for a quick victory rush.
Heroic throw is mostly useless as a DPS tool, but it can provide you with some extra damage. If you find yourself with an open GCD, but without any procs up, or any rage to ms or slam, it can be used as a minor damage boost.
Watch your threat, manage your global cooldowns, and choose your ability used based on what you have available to you, and how much rage you have, and you'll do fine. Good luck!