Aggro management is all about proper positioning. It might seem like a good idea to have your tanks and melee up front while your ranged classes hang way in the back, but this usually isn't the case. In this situation, if you pull aggro during a fight the tank will be too far away to quickly reapply a taunt and you might have to absorb a couple of hits before you are in the clear. I find it a lot better to keep ranged classes within about 10-15 feet of the tank, well within taunt range. This also has the added benefit of making it easier to dispel and barrier the whole group.
Keeping a mage w/ an upgraded barrier spell also greatly helps to reduce incoming damage. It's saved my ass several times in fights that have come down to the wire.
Also don't forget to use stealth... it can be easy to forget/overlook it in the midst of combat. I'm also playing as an archer, I will usually start a fight w/ full-draw + aimed shot then I pop cloak which basically just resets the aggro.
Hope this helps.