This is my raid spec.
http://talent.mmo-champion.com/?warr...&version=10048
Use this or something similar.
Don't get caught up 100% in your DPS b/c an arms warrior brings a lot more to the table. (demo shout, thunder clap debuff, commanding shout, sunder armor, shattering throw, bloodfrenzy etc.) But since DPS is your concern that's what I will address.
Always keep rend up. I suggest Glyphing into it to free up some GCD's. Use execute and overpower whenever they proc. Try to keep MS on cool down. and only after those are all on CD do you spam IMPROVED slam. Don't worry about Heroic Strike just yet. Get your rotation down set so it's second nature, then start playing around with it. b/c a mistimed HS can rage starve you for 3+ seconds leaving you with just ur d**k in your hands.
As for particulars to boost your DPS, know when heroism will be used. Try to time it so that bladestorm is either saved for it, or so that you can use it early and have it back up for Hero. In addition, a nice shattering throw on the boss right b4 hero is a great way to boots RAID DPS.
Recklessness is a little tricky b/c you don't want to blow all your rage switching stances. There are some fights where I don't sure it, and some where I make SURE I use it. Any time there is an "area buff" like Malygos sparks or when you're fully clustered on Thaddius, burn your rage down productively and then switch to it. a short string of 20-35k crits will more than make up for the stance dancing. (switch back to arms b4 you use ur "guaranteed crit" attacks so you can quickly build your rage back up.)
As for grouped clusters, this is where your imp demo shout and thunderclap will make you more useful as a raid member and put you in the back seat as a DPSer. Ret Pallys, Mages, DKs, Warlocks, Balance Droods... they have AoE that you cannot match. So don't fret about it. Thunder clap, sweeping strikes. Don't even bother with bladestorm unless you KNOW you'll have it up by the time you really need it.
I hope that some of these tips help. Remember, you can be a very valued raid member w/o always being #1 on the DPS charts. The good raiders and raid leaders will will recognize the little things that you're doing.