From here I offer only advice. In the first section where you fight the waves of enemies head back to where you come into that section at and fight your way through the captains and snipers and dregs and repeat whenever a new wave shows up. For the tank focus on avoiding the tank while killing the adds. Once the adds are down go after the tank and repeat. For sepics just go to the room on the left of the fight area and kill the adds and then shoot the boss and repeat. Good luck!