I just started using this website to track some items for my guild and I noticed your post when i hit the warrior section. The prior answer of going to Tankspot is a really good recommendation as there is a wealth of knowledge there.
Additionally, from my own experiences, tanking trash and bosses uses a slightly different opening rotation. The first thing I ensure in my raids is that my healers all have tank assignments for trash clearing. It keeps them focused on you and lets you be a little more aggressive on pulls then you may normally not be. With this in mind, you charge into a pack of mobs and immediately Thunderclap. I typically take a step back to bring the mobs tighter together and then i Shockwave them. I queue up a Cleave, toss a demo shout, Revenge, switch targets, shield slam, switch targets, cleave, Thunderclap, Revenge/SS etc.
The key to this is to work the same rotation on multiple targets and use your AE style abilities quickly. Working one target and expecting to hold a pack of 4-5 is not going to work. I run mainly with Mages, warlocks, Fury warriors, and rogues with liberal use of Fan of Knives so my OT and I have to be quick and work rotations on many mobs. I dont really have a Paladin or DK tank that plays regularly and maybe that is why we got really good at holding the mobs. We don't have that AE crutch.
However, as a warrior you are what i call Mobile AE, or a Mobile Consecrate! Your Shockwave and TC arent tied to a spot on the floor so you can be everywhere at once; especially with the changes to Intercept, Charge, and intervene. We can use them in any stance so do forget that as a mobility tool!
For single target threat use your vigilance on a top-notch single target DPSer. Don't look at who is doing mad AE threat but look at that guy that is always creeping up. There is not much of a rotation anymore but learn and use the priority system. Rev - SS - Dev - (Conc/SW etc). We have a lot of tools and your issues could be a multitude of reasons.
I would also look at your self from an itemization perspective. I do not know your gear or how your gear stacks against your DPS's gear but make sure you are itemized right. Not being hit capped or expertise soft capped will hurt you a great deal on threat generation. The Deep Wounds spec will offer you a natural Threat increase on trash; procs off your damage shield. Also, check your glyphs. If you are more concerned about Trash threat then Single target threat then look at the glyph of sunder which applies a stack of sunder to a nearby mob. If you care more about single target threat, as i do, then use glyph of devastate. This will apply 2 stacks of sunder to your target every time you click the button.
Our use of devastate is limited since WOTLK hit. We use it mainly to proc Sword and Board. It is still valuable in the rotation but typically when our other priorities are on GCD. Lastly, make sure that you aren't getting overzealous with heroic strike spam on trash. This is a good way to rage dry yourself putting you in a position of just standing there doing nothing waiting for rage while your DPS are gaining valuable ground.
Grab omen threat meter if you do not have it. there is a TPS column. Go out and find some mobs that you can beat of for a bit that wont kill you right away or take a healer with you. Get an idea of how much average Threat Per Second you are pushing. 4-6k should get you well past most DPS. In current gear i can spike around 9k TPS then its back down to around 5-6k depending on rage flow.
Hope this helps and good luck.
