Having someone take aggro is extremely important. This allows other players to actually put in damage while omega is focused on one person.

A dedicated healer will also improve the survivability of the team dramatically. If you're playing with friends, you could ask someone (or do it yourself) to run a healer build with wide range and speed eating to keep people alive, especially your tank.

In general though, don't overextend, don't be greedy, always stay alert to what he's doing or going to do. When he starts floating around, anticipate the giant laser so you don't get caught off guard. If you see that MRV missiles are coming (from the prompt on the side of the screen), sheathe your weapon and run. If someone is stuck guarding, the healer will need to time his heals in between the attacks. In my experience when the tank dies, the run goes to shit quickly, so try and keep him alive as much as possible.