Copied my TrueAchievements solution and am posting it here.Before even joining the dungeon, please learn your class. Cant tell you how many times I've played with Tanks who dont know how to tank. It will be a lot easier on EVERYONE if you know your roll in a group.
Bastion of Lok (BoL) is the first dungeon, or instance, you'll have access to. As such, it isn't very difficult, the dungeon consists of mostly weak enemies that, as long as you don't rush, are easy to kill.
Tetra Aniask
*** Spoiler - click to reveal ***Stay out of the red if you're DPS, Tank should assault her at all times, and Healers should keep a generous distance in case healing causes her to focus on them. She is more or less like the other Devan you've fought.
Soulcrusher
*** Spoiler - click to reveal ***He will appear after Tetra's death. Soul has some powerful attacks, including a spin move that will hit all players within about 5m of him, a leaping smash that will stun the player if hit, and a fireball attack. Tanks should stay close and keep his attention, while DPS chips away, and Healer should be healing the Tank (and if you have debuffs, apply them when able, if you're a Mystic, be sure to drop MP orbs as well).
After his death, head back to the chamber with all of the little guys you killed earlier, the door on the right side of the room is now open
Bloodbound Vulcan
*** Spoiler - click to reveal ***Blood acts similarly to Soulcrusher, similar attack patterns, minus the fireball, which is replaces by a rushing attack that will trample and damage players as long as they are in the way. A prompt will appear when he is about to do his jump attack, so watch for it and be ready to move.
Most players are getting the achievement after defeating him, even though there's another boss that appears when he reaches 10% HP.
Murdranak
*** Spoiler - click to reveal ***He doesn't have any noticeable special skills, and dies fairly quickly compared to Bloodbound. Just keep attacking, and he'll go down quick.
If you'd like a video guide, here's one. This is from a Mystic point of view, but it gives you a good idea what to expect.