Achievement 'Triple Rez' worth 10 Gamerscore.
You can get this achievement by playing any race, although for resurrecting people I recommend an Elf or a Dwarf.
When using resurrect, a yellow circle appears on the ground around you and moves with you. Anyone who is dead on your team in the circle will come back to life. Simply, cast resurrect when there are three dead ally's in your reach and there is your achievement.
First thing you need to do is buy Resurrect (Spell, 2000CR). After that its all kinda based on luck, though to boost your chances, try buying Gust (Spell, 2000CR). Now, use Gust on dead bodies to push them closer together, doing this makes it easier to get all three resurrects in one cast.
Other then that, you really just have to be in the right place at the right time.
*EDIT* A friend reminded me that bodies can be destroyed by shooting them, slicing them with the katana/artifact. Watch out for this when resurrecting people. You can destory bodies in the game modes 'Raid' and 'Extraction'; In the game mode 'Attrition', you must use the artifact to destroy bodies. The amount of health a body has until it is destroyed depends on the round win/loss difference. If you are losing, the dead ally's on your team, their bodies can withstand much more beat down then the team winning.