First and foremost, there is no rotation with a trooper; merely a priority list. The order is determined by your highest hitting abilities which is determined by your spec. I have increased elemental damage therefore my single target electric shock ability is a decent hitting one. Like others have said stockstrike is probably the hardest hitting especially when specced into. This is followed by the electric shock ability (apologize I forgot the name) and high impact bolt.
Second, as others have said one of the hardest things about tanking is getting aggro in the first place. Always be the one to initiate a fight. Never let your dps do so. If they do and you're far enough behind, let them die. Sounds harsh I know, but when I dps'd in other mmo's it taught me a lesson real quick.
Now, in regards to picking up aggro on multiple targets it all comes down to how they're spaced. If they're close enough always start with mortar volley for groups of 3 or more. 1 minute is a very small cooldown. Sticky grenade is an awesome way to get aoe aggro also. But is very much limited by how close or far apart mobs are. A neat trick with sticky grenade is throwing it on a distanced melee mob so that it runs towards you and blows up in the pack of mobs.
I've heard explosive surge mentioned and as much as I agree that it is a decent aoe ability. From my experience with it currently it drains your ammo practically too fast. As you all know ammo is our resource. What many of you may not know is that the four small arrows to the right of your ammo bar determine the speed of regeneration. The lower your ammo gets, the less arrows there are (out of a total of 4). So basically, if you burn up all your ammo with little or no regard (like using explosive surge repetitively) the longer it will take you to get ammo back. On that same note, the less you'll be able to use your special abilities. If you're stuck using hammer shot half a fight can you really hold aggro well? Your best bet is to keep your ammo high enough that you have 3-4 of the arrows left still or almost full speed regeneration. You can empty half your ammo bar, sometimes even more, and still have full speed regeneration if you rotate hammer shots in.
We have 2 taunts, 3 at once lvl 30, that we can use to get attention back to us. Keep in mind that taunt and harpoon are virtually the same minus the pull effect. Try to only harpoon ranged targets so that you can get them in range of your aoe or stockstrike. Melee targets you can just neural and they'll run to you as long as u at least hammer shot them after. I generally save harpoon for oh crap moments but it's up to you.
Finally, the best advice I can give any tank is to have a kill order. If you don't and you just go rushing in and taking everything to the face, you and your friends will die. Mark the farthest mob from the group or the most dangerous mob for cc. CC more if you can if not then set up a kill order on the elites using target markers. I'll use search and rescue (4m+ heroic on tatt) as an example because it is the first truly punishing set of elites i've faced if not approached properly. My rule of thumb is all grey mobs kill first always, no exceptions. This gives me time to round up the actual elites (usually theres only actually 3 or 4) while CC's go out and my group kills the grey non elites. Now if done properly I can still round up the whole group including non elites and keep them at least focused on me while my group kills them. Initial aoe will hold aggro on them long enough for the group to drop them (mortar volley and sticky). I then proceed to hit the first kill order target with stockstrike and electric shock and high impact bolt I then generally ion pulse the group of elites and then get started on the 2nd kill order target with high hitting abilities. Then I tab back to the first target and ion pulse/high hitting abilities everybody.
CD's:
Many tanks forget these exist or worse, they don't use them out of fear they'll need them later and thus end up almost never using them. Now as vanguards we have a lot of cd's. I'll go through each and list their pro's and cons.
Cryo-Grenade: Awesome for limiting incoming damage but only lasts 4 seconds : ( . Always use this on the hardest hitting mob right after aoe'ing/rounding up a group. Four seconds is a long time to get torn up by a hard hitting elite. This ability will make your healer love you and your chances of survivability go up drastically.
Shield: Again I apologize for forgetting the specific names of abilities. We have a shield that reduces incoming damage by 20%. Use it!! This is our "OH CRAP" save our own butts ability. It doesn't seem like much but it is. Especially if you use it in when you have multiple targets beating you down. This can drastically reduce incoming damage in those situations.
Smoke-bomb: Targets become 20% less accurate. Does this need to be explained? I'm amazed at how many people i've met overlook this ability. Getting hit 20% less is virtually the same as shield. I use this ability all the time. Again it works great with multiple targets (can anybody tell yet that we're aoe tanks?). Just remember do not use this if your mobs are spaced out decently or it will not hit them. This only works on very close mobs.
No Retreat: I may have completely butchered this ability's name. This is our 20 min. cooldown. Heals your over time and refreshes cry-grenade. This I only use if i'm so close to winning and also so close to dying. It heals me and lets me cc a mob again. Do not use this ability of you have little to no chance of surviving. It is a 20 minute cd.
Words of Advice
I'll be quick here as this post has gone longer than I expected lol.
As a tank you need to be aware of everything and everyone at all times. Is that pat coming our way? Should I line of site mid fight behind a corner to avoid the pat or should I harpoon it to us to avoid pulling other mobs. Is my healer getting hit? These are all things you need to notice and make decisions about on the fly. The best tank is often the one that gets the least credit. Nobody notices when things go flawlessly. I promise they will abuse you if they don't though:p. Shoot for being so ahead of the game that nobody even notices what you're doing. That ensures a smooth and flawless progression through any heroic or fp.
Taunts are not a pull method. To all of you tanks who think you open with a taunt, STOP IT! Look at aggro as a race. As you hit mobs you pull into the lead. As your dps hit mobs and your healer heals, they catch up to you. A taunt is a leapfrog to the front of the aggro race. However, if you start with a taunt it merely makes the mob run to you first but you still haven't even left the starting line. So if any of your team mates hit that mob they've just pulled ahead of you right off the bat. Use your taunts only to get back in the lead with aggro, not to start the race!
You can change who you have guard on all the time. Don't think its an ability you just leave on one person. If you have a hard aoe hitting team mate put guard on them before a big aoe fight. Single target dps teammate who's constantly nipping at your heals on a boss fight, guard him. Heals getting crit happy or simply running into random mobs like an air head, guard him. This ties back into my first advice of being aware.
If you have any questions feel free to ask. Hopefully I gave you a few pointers that help .
