Get all of the ship enhancements from the research bay. You also should speak with each teammate and ask for their opinions on upgrades for both the ship, and their own personal upgrades. During the Actual mission on the collector base, there comes a time where 4 of your squad mates must be selected for advancing into the base. these include a tech specialist, a 2nd squad leader, a biotic, and someone to take the survivors back to the ship. For the tech specialist choose Tali of Legion. the 2nd squad leader should be either Garrus or Jacob. The biotic should be Samara of Jack (Don't believe Miranda that "any biotic" can do it). Finally the person to take survivors back to the Normandy can be anyone but Jack, and they are also absent from the your own personal party should you choose them. Kill the final boss as quick as you can, and everyone should survive.