It's not really too terribly difficult until just right as you get to the last part. People keep suggesting to bring a defender and go all exotic swords while others suggest bringing AoE weapons like Telesto or Dragon's Breath. Personally, I've found it easier to just prioritize beforehand so you know who is using and doing what. Got a pal who's got good weapons to kill the Ultra? Focus on adds and switch out to an arc weapon for the Taken Centurions. Take turns using supers like if you have a Nightstalker set up as a tether-orb generator then focus on using the best of your damage-dealing AoE supers. Finally, make good use of your perks and abilities. A well-placed grenade or distanced melee can make quick work of enemies while you're using your primaries. Overall, just focus on your team at large and cooperate. At my best I've had about ten to twenty seconds remaining once we finished wiping out the last of those endless Psions. >,>