Since not a lot of people seem to be getting used to tank mechanics from a PvP standpoint, I figured I'd make a guide for players not used to PvP Tanking, especially Troopers. I happened to have a bit of experience with PvP Tanking, particularly with the mechanics Bioware is using as they are similar, if not the same as, Mythic's MMO Warhammer Online (Who were brought in to oversee this aspect of the game). First and simple: PvP Tanks are a hot commodity. 1. Because people who are not necessarily used to these mechanics do not see tanking as a viable pvp spec, and therefore do not roll them. 2. Tanks literally are the lynchpin to a good pre-made, they can stop a focus fire train singlehandedly, cc more easily than any other role keeping certain players contained, as well as leading assist trains making it much easier for dps to do their job. TLDR: Tanks are the first ones in, and make sure no one else is getting hit.
Tanking abilities in PvP work extremely similarly to tanking in PvE, the only difference is the things you tank have complete free will to do whatever the hell they want, so rather than say 'attack me' and them obeying your commands, it's 'attack me or you do no damage'.
The first tool Tanks should get used to is Taunt. It is your bread and butter for PvP Tanking, rather than saving it for when something goes awry it should be spammed ad nauseum. the reason is simple: it makes the target do less damage to anyone other than you. It is much more flexible than other protection abilities like cover as it targets the enemy 1v1 and debuffs them, making sure they can't hurt ANYONE but you (compared to say guard which really only protects one person.) If it isn't on constant cooldown, your simply not getting near the protection points you should.
Guard is your second real protection ability. like Taunt it works differently than PvE, it splits damage between you and another player, which when added to your mitigation stats as a tank, is usually considerably reduced. Guard should also be used a bit differently than PvE rather than a 'set it and forget it' tactic it should be actively shuffled between players to maximize protection. The general rule is follow the enemy, but you need to keep in mind about guard's range, walk too far from you ward and you will lose it. Guard also requires you to swap between targeting enemies and friendlies, making the job a bit harder in the heat of battle.
Crowd Control is the third type of 'Tanking' you come across. I mention Crowd Control because as a Tank, you recieve more diverse methods of keeping people contained than any other class. As a Trooper, your favored method of cc is the Harpoon ability. It let's you place enemies where you want allowing it to become a very flexible tool, whether it's pulling enemy dps off a running healer or pulling enemy healers into waiting dps. However not every cc ability you get is limited to stuns and cripples. With the proper speccing Explosive Surge and Smoke Grenade become very effective tools for keeping dps down, especially in large groups. With Static Field, Explosive Surge allows you consistently debuff enemy damage by 4%, when combined with Taunt and guard, it leaves just 16% of enemy damage getting through to their target without attacking you. Smoke Grenade reduces hit chance by 10%, becoming very annoying to faster striking dps (it is best saved for melee classes or dual wielders in groups). In short if given the choice between stock strike and cc, pick cc.
Remember: You goal is NOT to dps. This is left to other classes. your priorities should ALWAYS be getting people to hit you, keeping them controlled, and staying alive, in that order.
Your usual rotation going into combat as Vanguard PvP should be something like:
Taunt->Ion Pulse / Explosive Surge (Surge in Groups, Ion Pulse Singular Targets)->cooldown cc (in groups start with smoke grenade, singular targets should be stunned to set up on.)
Stock Strike and HiB should be relegated to Ammo dumps, in case not enough dps is being done. Your dps should be scondary to add just enough burst to kill an important target, otherwise save the ammo.
Reactive Shield should be saved for larger scale encounters (usually used at the beginning to set up). if in 1v1, Stun first, then use Shield out of the Stun.
Guard should be shuffled between rotations to whoever is taking damage. it takes a bit of skill to appropriately maximize your guard shuffling , something that comes with practice.
EDIT: Consolidated the post. ~Fluttershy